Enemy ai Multiple targets

I have been working on the following code and it works nice so far for what I am wanting but the issue I have hit is I want it to record if more then one enemy entered it's zone and if the first one dies or leaves zone switch to next if it is still in the zone.

Here is my code:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyAi : MonoBehaviour 
 {
     public Transform target;//Targets.
     public int moveSpeed;//Speed enemy can move.
     public int rotationSpeed;//Speed enemy can rotate.
     public int detectionDistance;//The distance the enemy can detect you from.
     
     
     
     
     private Transform myTransform;//Save for the transform.
     
     void Awake()
     {
         myTransform = transform;//This saves our transform so we dont have to look it up all the time.    
         target = myTransform;
     }
     
     void Start ()
     {
         
     }
     
     void Update ()
     {
         //float distance = Vector3.Distance(target.transform.position, transform.position);
         
         
     
         
         //if(distance < detectionDistance)
         //{
         myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(target.position - myTransform.position), rotationSpeed * Time.deltaTime);//Makes it look at us using the speed we set over time.
         
         //Move to player.
         myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
         //}
     }
     
      void OnTriggerEnter(Collider other) //When collided
     {
         if(other.tag == "Player")
         {
             target = other.transform;
         }
         
         
     }
     void OnTriggerExit(Collider other) //When collided
     {
         if(other.tag == "Player")
         {
             target = myTransform;
         }
         
         
     }
 }