how to enable/disable slider VIA script from a prefab

  Ive been working on a project and I recently came up with a problem. I want when my boss to spawn, to enable a slider which will indicate its health but as the boss is a prefab I cant access the disabled slider. Is there anyway I can do this?

Here is the script for my Boss and my bossSpawner:

  public class FirstBossBhv : MonoBehaviour{

  public playerStats PlayerStats;

  public float speed;
 
  public Transform bosspos;

  public GameObject projectile;

  private bool movingRight = true;

  private bool movingLeft = false;

 public Rigidbody2D rb2d;

 public float timeBTWshots = 2;


 public float timer;

 public Slider BossHealth;

 float Health = 100;

  bool isAlive = true;


 private void Start()
 {
     PlayerStats = GameObject.Find("player").GetComponent<playerStats>();
     BossHealth = GameObject.Find("Canvas").GetComponent<Slider>();
 }

 void Update()
 {
     if (movingRight == true)
     {
         rb2d.velocity = transform.right * speed;
     } else if (movingLeft == true)
     {
         rb2d.velocity = transform.right * -speed;
     }

     timer += Time.deltaTime;
     if(Mathf.Round(timer) == timeBTWshots)
     {
                         Instantiate(projectile,bosspos.position,Quaternion.identity);
         timer = 0;
     }

     if(Health == 0)
     {
         isAlive = false;
         Destroy(this.gameObject);
     }

     if(isAlive == true)
     {
         BossHealth.gameObject.SetActive(true);
     }else if(isAlive == false)
     {
         BossHealth.gameObject.SetActive(false);
     }

     BossHealth.value = Health;


 }

 private void OnCollisionEnter2D(Collision2D collision)
 {
     if (collision.gameObject.CompareTag("2Walls"))
     {
         if (movingRight == true && movingLeft == false)
         {
             movingRight = false;
             movingLeft = true;
         } else if (movingRight == false && movingLeft == true)
         {
             movingRight = true;
             movingLeft = false;
         }
     }

     if (collision.gameObject.CompareTag("pLAYER"))
     {
         Health -= PlayerStats.dmg;
     }
 }

}

 public class BossSpawn : MonoBehaviour
 {

 public GameObject boss;

 playerStats PlayerStats;

 enemySpawner EnemySpawner;

 void Start()
 {
     PlayerStats =  GameObject.Find("player").GetComponent<playerStats>();
     EnemySpawner =    GameObject.Find("Spawner").GetComponent<enemySpawner>();
 }
 void Update()
 {
     if(PlayerStats.score == 2 && EnemySpawner.Waves == true)
     {
         PlayerStats.score = 0;
         EnemySpawner.Waves = false;
         StartCoroutine(bossApperance());
     }
  }

 IEnumerator bossApperance()
 {
     yield return new WaitForSeconds(5);
       Instantiate(boss,this.transform.position,Quaternion.identity);
 }