Prevent spawn object at the same position from a list.

Hello everyone, i am brand new to both unity and coding, I am trying to prevent my spwaner to spawn objects from my list at the same position in a row but i couldnt do it. I also made a search on the forum and saw some other topics on this problem but couldnt apply those solutions into my code.

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using TMPro;
5. using UnityEngine;
6. using UnityEngine.SceneManagement;
7. using UnityEngine.UI;
8.  
9. public class GameManager : MonoBehaviour
10.  
11. //spawnera alternatif daha güzel
12. {
13.     public List<GameObject> targets;
14.  
15.     // Start is called before the first frame update
16.     private int score;
17.     private int i = -1;
18.     public TextMeshProUGUI scoreText;
19.     public TextMeshProUGUI gameOverText;
20.     public Button restartButton;
21.     public bool isGameActive;
22.     public float spawnRate = 3.0f;
23.     public float scoreRate = 4.0f;
24.  
25.  
26.  
27.     void Start()
28.     {
29.         isGameActive = true;
30.         score = 0;
31.         UpdateScore(0);
32.         StartCoroutine(SpawnTarget());
33.      
34.        
35.  
36.     }
37.     IEnumerator  SpawnTarget()
38.     {
39.         while (isGameActive)
40.         {
41.             yield return new WaitForSeconds(spawnRate);
42.             int index = Random.Range(0, targets.Count);
43.             Instantiate(targets[index]);
44.  
45.          
46.                 UpdateScore(5);
47.            
48.          
49.         }
50.     }
51.     // Update is called once per frame
52.     public void UpdateScore(int scoreToAdd)
53.     {
54.  
55.         score += scoreToAdd;
56.         scoreText.text = "Score: " + score;
57.  
58.     }
59.  
60.     public void GameOver()
61.     {
62.         restartButton.gameObject.SetActive(true);
63.         gameOverText.gameObject.SetActive(true);
64.         isGameActive = false;
65.         Time.timeScale = 0;
66.  
67.  
68.     }
69.     public void RestartGame()
70.     {
71.         SceneManager.LoadScene(SceneManager.GetActiveScene().name);
72.         Time.timeScale = 1;
73.        
74.        
75.     }
76.    
77.   }
78.  
79.  
80.  
81.