Variable not affecting spawned in gameObject

I'm kind of new to C# so I probably made a silly mistake, but my variable is not affecting a spawned in enemy. I want the player to be able to upgrade its damage and then be able to do more damage to enemies, however, when i'm playing the game and I upgrade its damage, the damage does increase in the prefab, however, the already spawned in enemies are stuck on the original damage and is not changing. How do I fix this? Please ask if you need more code or have and questions.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.AI;
 using TMPro;
 
 public class EnemyDamage : MonoBehaviour
 {
     public int health = 8;
 
     public Transform target;
     private NavMeshAgent enemy;
     
     public Transform bulletSpawnPoint;
     public GameObject bulletPrefab;
     public float bulletSpeed = 8f;
 
     bool playerIsCloseEnough = true;
     float distance;
 
     public GameObject protons;
 
     public GameObject elementDrop;
 
     public ParticleSystem hurtEffect;
 
     public int dropAmount;
 
     public ShootBullet shootBulletScript;
 
     public int playerDamage = 1;
 
     // Start is called before the first frame update
     void Start()
     {
         StartCoroutine(EnemyFire());
     }
 
     void Awake()
     {
         enemy = GetComponent<NavMeshAgent>();
     }
 
     // Update is called once per frame
     void Update()
     {
         distance = Vector3.Distance(target.transform.position, transform.position);
         if(distance <= 30)
         {
             playerIsCloseEnough = true;   
         } 
     }
 
     IEnumerator EnemyFire()
     {
         while(playerIsCloseEnough)
         {
             if(playerIsCloseEnough)
             {
                 target = GameObject.FindGameObjectWithTag("Player").transform;
                 GetComponent<NavMeshAgent>().destination = target.position;
 
                 var bullet = Instantiate(bulletPrefab, bulletSpawnPoint.position, bulletSpawnPoint.rotation);
                 bullet.GetComponent<Rigidbody>().velocity = bulletSpawnPoint.forward * bulletSpeed;
                 yield return new WaitForSeconds(0.8f);
             }
         }
     }
 
     void OnTriggerEnter(Collider obj)
     {
         if(obj.gameObject.tag == "Player")
         {
             Instantiate(hurtEffect, transform.position, transform.rotation);
             health = health - playerDamage;
             if(health <= 0)
             {
                 Destroy(gameObject);
                 for (int i = 0; i < dropAmount; i++)
                 {
                     Instantiate(protons, transform.position, transform.rotation);
                 }
                 Instantiate(elementDrop, transform.position, transform.rotation);
             }
         } 
 
         if(obj.gameObject.tag == "Bullet")
         {
             Instantiate(hurtEffect, transform.position, transform.rotation);
             health = health - playerDamage;
             if(health <= 0)
             {
                 Destroy(gameObject);
                 for (int i = 0; i < dropAmount; i++)
                 {
                     Instantiate(protons, transform.position, transform.rotation);
                 }
                 Instantiate(elementDrop, transform.position, transform.rotation);
             }
         }
     }
 }