Always check OnTriggerEnter

How do I check if an object is in the trigger area, but I want to check it every frame. I tried the usual way to do it but when I enter it just moves once instead of like in the update function, anyway here is my script:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyHealth : MonoBehaviour {
 
     public int health;
     public Transform player;
 
     // Use this for initialization
     void Start () {
     }
     
     // Update is called once per frame
     void Update () {
         if (health <= 0) {
             Destroy (gameObject);
         }
     }
 
     void OnTriggerEnter (Collider other) {
         if (other.gameObject.tag == "Player") {
                     //I want it to move every frame as long as it is in the trigger
             transform.position += new Vector3 (-player.position.x, transform.position.y, -player.position.z);
         }
     }
 
     void OnTriggerExit (Collider other) {
         
     }
 }