How to assign GameObject to a instantiated prefab via Script(C#)?

I am trying to have a popup canvas on trigger to show Level complete. My game is using instantiated prefabs for the characters. When I drop the character into the scene and pass through the trigger it works and the canvas will popup. But when I try this with the prefab, it is not finding the canvas to popup. I have tried -

LvlComplete = GameObject.FindWithTag("lvl");

LvlComplete = GameObject.Find("LVL Complete");

And neither of these seem to work. Any ideas what I can try to get the prefab to find the canvas/gameobject in the scene?

Thanks for the help!

Here is the script Im using using UnityEngine; using System.Collections; using UnityEngine.UI; using System;

 public class Timer : MonoBehaviour
 {
     
     private float secondsCount;
     private int minuteCount;
     private Text ScoreText;
     public float startTimer = 0;
     public GameObject LvlComplete;
    
     
 
     
 
 
     public void Awake()
     {
         ScoreText = FindObjectOfType<Text>();
         
         //LvlComplete = GameObject.FindWithTag("lvl");
         LvlComplete = GameObject.Find("LVL Complete");
 
     }
 
 
         void Update()
     {
         
         
 
         if (startTimer > 0)
         {
             
             SumScore.Add(Mathf.RoundToInt(Time.deltaTime * 100)); // This adds the delta time to the score as an int (in hundredths of a second)
         
             var minutes = (SumScore.Score / 100) / 60; //Divide the guiTime by sixty to get the minutes.
             var seconds = (SumScore.Score / 100) % 60; //Use the euclidean division for the seconds.
             var fraction = (SumScore.Score) % 100;
 
             //update the label value
             
         }
         else
         {
             
         }
     }
 
 
     
     void OnTriggerEnter(Collider other)
     {
 
         if (other.tag == "Start")
         {
             
             setTimer(1);
         }
 
         if (other.tag == "Finish")
         {
             
             SumScore.SaveHighScore();
             setTimer(0);
              LvlComplete.SetActive(true);
 
 
 
 
 
 
         }
 
     }
 
     void setTimer(int t)
     {
         Timer playerTimer = this.GetComponent<Timer>();
         playerTimer.startTimer = t;
         
     
 
     }
 
    
 
     }