I'm just I'm trying to destroy the copies of the prefab not the actual prefab

Questions & Answers
1

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

public class AaP : MonoBehaviour
{
// Start is called before the first frame update
void Start()
{

}

// Update is called once per frame
void Update()
{
    if (transform.position.z > 50)
    {
        Destroy(gameObject);
    }
}

}

2

The variable gameObject should contain an instantiation of the prefab.

GameObject newGameObject = Instantiate(gameObject);