How do i kill my player and restart him

I'm trying to make an endless runner and I get everything working except the kill box here is some of my code its c#

this is my game manager :

 using UnityEngine;
 using System.Collections;
 
 public class GameManager : MonoBehaviour {
 
     public Transform platformGenerator;
     private Vector3 platformStartPoint;
 
     public PlayerController thePlayer;
     private Vector3 playerStartPoint;
 
     // Use this for initialization
     void Start () {
         platformStartPoint = platformGenerator.position;
         playerStartPoint = thePlayer.transform.position;
 
     
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     public void RestartGames()
     {
         StartCoroutine ("RestartGameCo");
     }
 
     public IEnumerator RestartGamesCo()
     {
         thePlayer.gameObject.SetActive (false);
         yield return new WaitForSeconds (0.5f);
         thePlayer.transform.position = playerStartPoint;
         platformGenerator.position = platformStartPoint;
         thePlayer.gameObject.SetActive (true);
     }
 }
 

and here is my character controller

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour {
 
     public float moveSpeed;
     public float speedmultiplier;
 
     public float speedincreaseMilestone;
     private float speedMilestoneCount;
 
 
     public float jumpForce;
 
     public float jumpTime;
     private float jumpTimeCounter;
 
     private Rigidbody2D myRigidbody;
 
 
     public bool grounded;
     public LayerMask whatIsGround;
     public Transform groundCheck;
     public float groundCheckRadius;
 
     //private Collider2D myCollider;
 
     private Animator myAnimator;
 
     public GameManager theGameManager;
 
     // Use this for initialization
     void Start () {
         myRigidbody = GetComponent<Rigidbody2D>();
 
         //myCollider = GetComponent<Collider2D>();
 
         myAnimator = GetComponent<Animator>();
 
         jumpTimeCounter = jumpTime;
 
         speedMilestoneCount = speedincreaseMilestone;
     }
     
     // Update is called once per frame
     void Update () {
 
         //grounded = Physics2D.IsTouchingLayers(myCollider, whatIsGround);
 
         grounded = Physics2D.OverlapCircle(groundCheck.position, groundCheckRadius, whatIsGround);
 
         if(transform.position.x > speedMilestoneCount) 
         {
             speedMilestoneCount += speedincreaseMilestone;
 
             speedincreaseMilestone = speedincreaseMilestone * speedmultiplier;
             moveSpeed = moveSpeed * speedmultiplier;
         }
 
         myRigidbody.velocity = new Vector2 (moveSpeed, myRigidbody.velocity.y);
 
         if(Input.GetKeyDown (KeyCode.Space) || Input.GetMouseButtonDown (0)) {
             if (grounded) 
             {
                 myRigidbody.velocity = new Vector2 (myRigidbody.velocity.x, jumpForce);
             }
         }
 
         if(Input.GetKey (KeyCode.Space) || Input.GetMouseButton (0)) 
         {
             if(jumpTimeCounter > 0)
             {
                 myRigidbody.velocity = new Vector2 (myRigidbody.velocity.x, jumpForce);
                 jumpTimeCounter -= Time.deltaTime;
             }
         }
 
         if(Input.GetKeyUp (KeyCode.Space) || Input.GetMouseButtonUp (0)) 
         {
             jumpTimeCounter = 0;
         }
 
         if(grounded) 
         {
             jumpTimeCounter = jumpTime;
         }
 
         myAnimator.SetFloat ("Speed", myRigidbody.velocity.x);
     }
 
     void onCollisionEnter2D (Collision2D other)
     {
         if(other.gameObject.tag == "killbox") 
         {
             theGameManager.RestartGames();
         }
     }
 }

plz help