Launch animation from button on instantiated object.

Hi, I hope I can make this as clear as possible.

I can't find out how I can bind the Onclick button to an animator in a prefab. What I mean is when the scene has started there is nothing except the ui with button and the camera. When I press a button a monster apears (it has been Instantiated and so I have a clone of the prefab) in this monster I have my animator ocmponent with animations in it.

I have a second button and when I press it nothing works. Here is where I have my plublic function to call when the button is pressed (TakeAction):

 public class ManageArthas : MonoBehaviour
 {
     
     private Animator arthasAnimator;
     private string[] actions = { "Walk", "Attack", "Channel", "Ready" };
     private int actionToStop = -1;
 
     // Update is called once per frame
     void Update()
     {
         arthasAnimator = GetComponent<Animator>();
         if (arthasAnimator.GetBool("Walk"))
             transform.Translate(Vector3.left * .9f * Time.deltaTime);
     }
 
     /// <summary>
     /// Makes Arthas look at the camera.
     /// </summary>
     public void Lookat()
     {
         transform.LookAt(Camera.main.transform.position);
         transform.eulerAngles = new Vector3(0, transform.eulerAngles.y + 90, 0);
     }
 
     /// <summary>
     /// Stops the action animations and plays the wait animation.
     /// </summary>
     private void Stop()
     {
         if (actionToStop >= 0)
             arthasAnimator.SetBool(actions[actionToStop], false);
         arthasAnimator.SetBool("Stop", true);
         actionToStop = -1;
     }
 
     /// <summary>
     /// action is between 0 and 3. Stops the wait animation and set the action animation then stops it after 3 seconds.
     /// </summary>
     /// <param name="action"></param>
     public void TakeAction(int action)
     {
         arthasAnimator = GetComponent<Animator>();
         if (actionToStop < 0)
         {
             actionToStop = action;
             arthasAnimator.SetBool("Stop", false);
             arthasAnimator.SetBool(actions[action], true);
             Invoke("Stop", 3);
         }
     }
 }

This class is a component of my monster (Arthas) So when I link from the onclick button TakeAction with number 0, nothing happens. I tried putting arthas from when the scene starts (and linking the arthas from the scene to the button) and it works.

My question is how do I link the instasiated arthas to the button ?

I hope I was clear enough :)

Thans for the help !