Question How to assign a canvas image to a variable of type GameObject

I'm trying to pass an image that will be my game over screen over the gameObject consists of an image with a button and a text inside

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5. using UnityEngine.UI;
6. using TMPro;
7.  
8.  
9. public class GameController : MonoBehaviour
10. {
11.     public int total_score;
12.     public TextMeshProUGUI scoreText;
13.     public static GameController instance;
14.     public GameObject game_over;
15.     // Start is called before the first frame update
16.     void Start()
17.     {
18.         instance = this;
19.     }
20.  
21.     public void updateScoreText()
22.     {
23.         scoreText.text = total_score.ToString();
24.     }
25.  
26.     public void showGameOver()
27.     {
28.         game_over.SetActive(true);
29.     }
30. }
31.