match one card and other cards

Halo developer, I made a memory game. but I want to make it match card A with B, card C with D, does not match Card A with Card A too. what should i do, and what should i add? I am very grateful if anyone wants to help me

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 
 public class GameControllerMM : MonoBehaviour
 {
     [SerializeField]
     private Sprite bgImage;
 
     public Sprite[] puzzles;
 
     public List<Sprite> gamePuzzles = new List<Sprite>();
 
     public List<Button> btns = new List<Button>();
 
     private bool firstGuess, secondGuess;
 
     private int countGuesses;
     private int countCorrectGuesses;
     private int gameGuesses;
 
     private int firstGuessIndex, secondGuessIndex;
 
     private string firstGuessPuzzle, secondGuessPuzzle;
 
     void Awake()
     {
         puzzles = Resources.LoadAll<Sprite>("Aset/memorygame");
     }
 
     void Start()
     {
         GetButtons();
         AddListeners();
         AddGamePuzzles();
         Shuffle(gamePuzzles);
         gameGuesses = gamePuzzles.Count / 2;
     }
 
     void GetButtons()
     {
         GameObject[] objects = GameObject.FindGameObjectsWithTag("PuzzleButton");
 
         for (int i = 0; i < objects.Length; i++)
         {
             btns.Add(objects[i].GetComponent<Button>());
             btns[i].image.sprite = bgImage;
         }
     }
 
     void AddGamePuzzles()
     {
         int looper = btns.Count;
         int index = 0;
 
         for (int i = 0; i < looper; i++)
         {
 
             if (index == looper / 2)
             {
                 index = 0;
             }
             gamePuzzles.Add(puzzles[index]);
             index++;
         }
     }
 
     void AddListeners()
     {
         foreach (Button btn in btns)
         {
             btn.onClick.AddListener(() => PickAPuzzle());
         }
     }
 
     public void PickAPuzzle()
     {
 
         if (!firstGuess)
         {
 
             firstGuess = true;
 
             firstGuessIndex = int.Parse(UnityEngine.EventSystems.EventSystem.current.currentSelectedGameObject.name);
 
             firstGuessPuzzle = gamePuzzles[firstGuessIndex].name;
 
             btns[firstGuessIndex].image.sprite = gamePuzzles[firstGuessIndex];
 
         }
         else if (!secondGuess)
         {
 
             secondGuess = true;
 
             secondGuessIndex = int.Parse(UnityEngine.EventSystems.EventSystem.current.currentSelectedGameObject.name);
 
             secondGuessPuzzle = gamePuzzles[secondGuessIndex].name;
 
             btns[secondGuessIndex].image.sprite = gamePuzzles[secondGuessIndex];
 
             countGuesses++;
 
             StartCoroutine(CheckIfThePuzzlesMatch());
 
         }
     }
 
     IEnumerator CheckIfThePuzzlesMatch()
     {
         yield return new WaitForSeconds(1f);
 
         if (firstGuessPuzzle == secondGuessPuzzle)
         {
             yield return new WaitForSeconds(.5f);
 
             btns[firstGuessIndex].interactable = false;
             btns[secondGuessIndex].interactable = false;
 
             btns[firstGuessIndex].image.color = new Color(0, 0, 0, 0);
             btns[secondGuessIndex].image.color = new Color(0, 0, 0, 0);
 
             CheckIfTheGameIsFinished();
         }
         else
         {
             btns[firstGuessIndex].image.sprite = bgImage;
             btns[secondGuessIndex].image.sprite = bgImage;
         }
         yield return new WaitForSeconds(.5f);
 
         firstGuess = secondGuess = false;
     }
 
     void CheckIfTheGameIsFinished()
     {
         countCorrectGuesses++;
 
         if (countCorrectGuesses == gameGuesses)
         {
             Debug.Log("Game Finished");
             Debug.Log("It took you " + countGuesses + "many guess(es) to finish the game");
         }
     }
 
     void Shuffle(List<Sprite> list)
     {
         for (int i = 0; i < list.Count; i++)
         {
             Sprite temp = list[i];
             int randomIndex = Random.Range(i, list.Count);
             list[i] = list[randomIndex];
             list[randomIndex] = temp;
         }
     }
 }
 
 ![using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class AddButtonMM : MonoBehaviour
 {
 
     [SerializeField]
     private Transform puzzleField;
 
     [SerializeField]
     private GameObject btn;
 
     void Awake()
     {
         for (int i = 0; i < 40; i++)
         {
             GameObject button = Instantiate(btn);
             button.name = "" + i;
             button.transform.SetParent(puzzleField, false);
         }
     }
 }][1]
 

[1]: /storage/temp/128307-card.jpg