Pathfinding AI with Aron Granberg, Prefabs with AI not Retaining Target Transform, Trying to change for AI to Follow GameObjects with Tag "Player" PLZ HELP

I'm making a top down shooter where zombies have to follow the player and waves of zombies come through the windows similar to COD:zombies. Whenever I have the prefab inspector tool open in unity however it doesn't let me set the player as a target. It only allows me to do so after the zombies have spawned in. I think setting the AI to follow a tag would fix it but I'm fairly new to coding. Any help?

 //My Code That Doesn't Work
 using UnityEngine;
 using System.Collections;
 
 namespace Pathfinding {
     /// <summary>
     /// Sets the destination of an AI to the position of a specified object.
     /// This component should be attached to a GameObject together with a movement script such as AIPath, RichAI or AILerp.
     /// This component will then make the AI move towards the <see cref="target"/> set on this component.
     ///
     /// See: <see cref="Pathfinding.IAstarAI.destination"/>
     ///
     /// [Open online documentation to see images]
     /// </summary>
     [UniqueComponent(tag = "ai.destination")]
     [HelpURL("http://arongranberg.com/astar/docs/class_pathfinding_1_1_a_i_destination_setter.php")]
     public class AIDestinationSetter : VersionedMonoBehaviour {
         /// <summary>The object that the AI should move to</summary>
         public Transform target;
         IAstarAI ai;
 
         void OnEnable () {
             ai = GetComponent<IAstarAI>();
             // Update the destination right before searching for a path as well.
             // This is enough in theory, but this script will also update the destination every
             // frame as the destination is used for debugging and may be used for other things by other
             // scripts as well. So it makes sense that it is up to date every frame.
             if (ai != null) ai.onSearchPath += Update;
         }
 
         void OnDisable () {
             if (ai != null) ai.onSearchPath -= Update;
         }
 
         /// <summary>Updates the AI's destination every frame</summary>
         void Update () 
         {
             player = GameObject.FindWithTag("Player").transform;
             if (player != null && ai != null)
             {
                 ai.destination = player.position;
             }
         }
     }
 }
 
 // The Original
 sing UnityEngine;
 using System.Collections;
 
 namespace Pathfinding {
     /// <summary>
     /// Sets the destination of an AI to the position of a specified object.
     /// This component should be attached to a GameObject together with a movement script such as AIPath, RichAI or AILerp.
     /// This component will then make the AI move towards the <see cref="target"/> set on this component.
     ///
     /// See: <see cref="Pathfinding.IAstarAI.destination"/>
     ///
     /// [Open online documentation to see images]
     /// </summary>
     [UniqueComponent(tag = "ai.destination")]
     [HelpURL("http://arongranberg.com/astar/docs/class_pathfinding_1_1_a_i_destination_setter.php")]
     public class AIDestinationSetter : VersionedMonoBehaviour {
         /// <summary>The object that the AI should move to</summary>
         public Transform target;
         IAstarAI ai;
 
         void OnEnable () {
             ai = GetComponent<IAstarAI>();
             // Update the destination right before searching for a path as well.
             // This is enough in theory, but this script will also update the destination every
             // frame as the destination is used for debugging and may be used for other things by other
             // scripts as well. So it makes sense that it is up to date every frame.
             if (ai != null) ai.onSearchPath += Update;
         }
 
         void OnDisable () {
             if (ai != null) ai.onSearchPath -= Update;
         }
 
         /// <summary>Updates the AI's destination every frame</summary>
         void Update () 
         {
             if (target != null && ai != null)
             {
                 ai.destination = target.position;
             }
         }
     }
 }