Target a GameObject and follow it when it's near

Hi Guys! I want to make a Strategy Zombie Survival RPG but, I have no idea how i shall make it work :/

It's Scripted in C#. I want the AI, Target a Tag when that tag Comes near. How shall i make it?

I've already got a Follow Script Here:

 using UnityEngine;
 using System.Collections;
 
 public class EnemyAI : MonoBehaviour
 {
     public int minRange;
     public bool follow;
     public float moveSpeed;
     public float rotationSpeed;
     private Transform myTransform;
     public Transform player;
 
     void Start()
     {
         myTransform = transform;
         player = GameObject.FindGameObjectWithTag("Player").transform;
     }
 
     void Update ()
     {
         if(player == null) {
             player = GameObject.FindGameObjectWithTag("Player").transform;
             if(player.name == "Cube (Transform)") {
                 player = GameObject.FindGameObjectWithTag("Player").transform;
             }
         }
         
         if(player != null && Vector3.Distance(player.position, myTransform.position) < minRange)
         {
             follow=true;
         }else{
             follow=false;
         }
 
         if(follow && player != null)
         {
             myTransform.rotation = Quaternion.Slerp(myTransform.rotation, Quaternion.LookRotation(player.position - myTransform.position), rotationSpeed * Time.deltaTime);
             myTransform.position += myTransform.forward * moveSpeed * Time.deltaTime;
         }
     }
 }