I need a game over(UI image) to appear after timer reaches 0

So here is my timer script that works fine. I need it to activate the game over(UI image ) when the timer reaches 0.I tried attaching a game over script to the UI image ( GOS script)….. no luck

using System.Collections; using System.Collections.Generic; using UnityEngine; using UnityEngine.UI;

public class Timer : MonoBehaviour { public Text gametimer; public float timeLeft; public GameObject Gameover; public Text gameovertext;

// Start is called before the first frame update void Start() {       }  // Update is called once per frame void Update() {     if (timeLeft > 0)      {         timeLeft -= Time.deltaTime;     }     else      {         timeLeft = 0;      }      displaytime(timeLeft);  } void displaytime(float timeToDisplay) {     if (timeToDisplay < 0)     {         timeToDisplay = 0;         Debug.Log("Game Ova YOung!!!");              }          float minutes = Mathf.FloorToInt(timeToDisplay / 60);     float seconds = Mathf.FloorToInt(timeToDisplay % 60);      gametimer.text = string.Format("{0:00}:{1:00}", minutes, seconds); }            } 

//////// Game over screen script below

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class GOS : MonoBehaviour { GameObject GameOverScreen; public Timer timer;

// Start is called before the first frame update void Start() {     timer = GetComponent<Timer>();     GameOverScreen.SetActive(false); }  // Update is called once per frame void Update() 

{ if (timer = null) { GameOverScreen.SetActive(true); }

} 

}