How do I get my Quit button to reset the score?

Hi - When I restart the game using the Quit button, it doesn't reset the scores and lives? What am I doing wrong? I included my Gameplay Controller and Game Manager script below. How do I get my Quit button to reset the score? Thank you for any help!

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.SceneManagement;
 
 public class GameManager : MonoBehaviour {
 
     public static GameManager instance;
 
     [HideInInspector]
     public bool gameStartedFromTitleScene, gameRestartedAfterPlayerDied;
 
     [HideInInspector]
     public int score, coinScore, lifeScore;
 
     void Awake () {
         MakeSingleton ();
     }
 
     void Start() {
         InitializeVariables ();
     }
 
 
     void OnEnable() {
         SceneManager.sceneLoaded += LevelFinishedLoading;
     }
 
     void Disable() {
         SceneManager.sceneLoaded -= LevelFinishedLoading;
     }
 
     void LevelFinishedLoading(Scene scene, LoadSceneMode mode) {
         if(scene.name == "GameplayScene") {
 
             if(gameRestartedAfterPlayerDied) {
 
                 GameplayController.instance.SetScore(score);
                 GameplayController.instance.SetCoinScore(coinScore);
                 GameplayController.instance.SetLifeScore(lifeScore);
 
                 PlayerScore.scoreCount = score;
                 PlayerScore.coinCount = coinScore;
                 PlayerScore.lifeCount = lifeScore;
 
             } else if(gameStartedFromTitleScene) {
                 PlayerScore.scoreCount = 0;
                 PlayerScore.coinCount = 0;
                 PlayerScore.lifeCount = 2;
 
                 GameplayController.instance.SetScore(0);
                 GameplayController.instance.SetCoinScore(0);
                 GameplayController.instance.SetLifeScore(2);
 
             }
         }
     }
 
     void InitializeVariables() {
         if (!PlayerPrefs.HasKey ("Game Initialized")) {
             
             GamePreferences.SetEasyDifficultyState(1);
             GamePreferences.SetEasyDifficultyCoinScore(0);
             GamePreferences.SetEasyDifficultyHighscore(0);
 
             GamePreferences.SetMediumDifficultyState(0);
             GamePreferences.SetMediumDifficultyCoinScore(0);
             GamePreferences.SetMediumDifficultyHighscore(0);
         
             GamePreferences.SetHardDifficultyState(0);
             GamePreferences.SetMediumDifficultyCoinScore(0);
             GamePreferences.SetHardDifficultyHighscore(0);
 
             GamePreferences.SetMusicState(0);
 
             PlayerPrefs.SetInt("Game Initialized", 123);
         
         }
 
     }
 
     void MakeSingleton() {
         if(instance != null) {
             Destroy(gameObject);
         } else {
             instance = this;
             DontDestroyOnLoad(gameObject);
         }
     }
 
     public void CheckGameStatus(int score, int coinScore, int lifeScore) {
 
         if(lifeScore < 0) {
 
             if (GamePreferences.GetEasyDifficultyState() == 1) {
 
                 int highScore = GamePreferences.GetEasyDifficultyHighscore();
                 int coinHighScore = GamePreferences.GetEasyDifficultyCoinScore();
 
                 if (highScore < score)
                     GamePreferences.SetEasyDifficultyHighscore(score);
 
                 if (coinHighScore < coinScore)
                     GamePreferences.SetEasyDifficultyCoinScore(coinScore);
 
             }
 
             if (GamePreferences.GetMediumDifficultyState() == 1) {
                                 
                 int highScore = GamePreferences.GetMediumDifficultyHighscore();
                 int coinHighScore = GamePreferences.GetMediumDifficultyCoinScore();
                                 
                 if (highScore < score)
                     GamePreferences.SetMediumDifficultyHighscore(score);
                                 
                 if (coinHighScore < coinScore)
                     GamePreferences.SetMediumDifficultyCoinScore(coinScore);
                                 
             }
 
             if (GamePreferences.GetHardDifficultyState() == 1) {
                                 
                 int highScore = GamePreferences.GetHardDifficultyHighscore();
                 int coinHighScore = GamePreferences.GetHardDifficultyCoinScore();
                                 
                 if (highScore < score)
                     GamePreferences.SetHardDifficultyHighscore(score);
                             
                 if (coinHighScore < coinScore)
                     GamePreferences.SetHardDifficultyCoinScore(coinScore);
                                 
             }
 
             gameStartedFromTitleScene = false;
             gameRestartedAfterPlayerDied = false;
 
             GameplayController.instance.GameOverShowPanel();
 
         } else {
 
             this.score = score;
             this.coinScore = coinScore;
             this.lifeScore = lifeScore;
 
 //            GameplayController.instance.SetScore(score);
 //            GameplayController.instance.SetCoinScore(coinScore);
 //            GameplayController.instance.SetLifeScore(lifeScore);
 
             gameStartedFromTitleScene = false;
             gameRestartedAfterPlayerDied = true;
 
             GameplayController.instance.PlayerDiedRestartTheGame();
         }
 
     }
 
 } // GameManager

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.SceneManagement;
 using UnityEngine.UI;
 
 public class GameplayController : MonoBehaviour {
 
     public static GameplayController instance;
 
     private AudioSource audioManager;
 
 //    [SerializeField]
 //    private AudioClip deadClip;
 
     [SerializeField]
     private Text scoreText, coinText, lifeText;
 
     [SerializeField]
     private GameObject pausePanel, gameOverPanel;
 
     [HideInInspector]
     public bool countScore;        
 
 
     void Awake () {
         MakeInstance ();
         Time.timeScale = 0f;
         audioManager = GetComponent<AudioSource> ();
 
     }
 
     void Start() {
     }
     
     void MakeInstance() {
         if(instance == null) {
             instance = this;    
         }
     }
 
     public void GameOverShowPanel() {
         gameOverPanel.SetActive (true);
 //        audioManager.clip = deadClip;
 //        audioManager.Play ();
 
     }
 
     public void PlayerDiedRestartTheGame() {
         StartCoroutine(PlayerDiedRestart ());
     }
 
     IEnumerator PlayerDiedRestart() {
         yield return new WaitForSeconds (1f);
 //        SceneManager.LoadScene ("GameplayScene");
         SceneFader.instance.LoadLevel ("GameplayScene");
     }
 
     public void SetScore (int score) {
         scoreText.text = " " + score;
     }
 
     public void SetCoinScore (int coinScore) {
         coinText.text = " " + coinScore;
     }
  
     public void SetLifeScore (int lifeScore) {
         lifeText.text = " " + lifeScore;
     }
 
     public void PauseTheGame() {
         Time.timeScale = 0f;
         pausePanel.SetActive (true);
     }
 
     public void ResumeGame() {
         Time.timeScale = 1f;
         pausePanel.SetActive (false);
     }
 
 //    public void quit() {
 //        Debug.Log ("has quit game");
 //        Application.Quit;
 //    }
 
     public void ReStartGame() {
         Time.timeScale = 1f;
         PlayerScore.coinCount = 0;
         PlayerScore.scoreCount = 0;
         PlayerScore.lifeCount = 2;
 
         GameplayController.instance.SetScore(0);
         GameplayController.instance.SetLifeScore(2);
         GameplayController.instance.SetCoinScore(0);
         SceneFader.instance.LoadLevel ("TitleScene");
     }
 
 
 } //GameplayController