void' is not an iterator interface type with collider "ERROR"

I was trying to remove a game object when you are interning a box collider, but my script is not working from some reason. I try to replace void whit IEnumerator but it give me a other error

"error CS1624: The body of DeathPit.OnTriggerEnter(UnityEngine.Collider)' cannot be an iterator block because void' is not an iterator interface type"

So can someone help me ?

 using UnityEngine;
 using System.Collections;
 
 public class DeathPit : MonoBehaviour {
 
     public GameObject sasa;
     
     void Start () 
     {
         sasa.SetActive (false);
     
     }
     
 
     void Update () 
     {
     
     }
 
     IEnumerator OnTriggerEnter(Collider broseidon)
     {
 
 
 
         if(broseidon.tag == "Player")
         {
             broseidon.transform.position = broseidon.GetComponent<Player>().checkPos;
             sasa.SetActive (true);
             yield return WaitForSeconds(0.5);
             sasa.SetActive (false);
 
 
         }
     }
 
 
 }
 

Here is the script