(beginner help?) Change an object's value inside an instantiated prefab's script?

Hello! I've recently begun making my first game in Unity, and have run into an issue with prefabs I don't really understand...
So, in my project I have an empty object "Spawner" with a "Spawner" script that spawns enemies above the screen at a set interval which then fall, and you need to shoot each one before they land on the player.

It's code is simple enough:

Code (CSharp):

1. private void Update()
2.     {
3.         if (respawnDelay <= 0)
4.         {
5.             Instantiate(enemies[rand], transform.position, Quaternion.identity);
6.             respawnDelay = respawnRate;
7.         }
8.         else
9.         {
10.             respawnDelay -= Time.deltaTime;
11.         }
12.     }

The enemies[] array is filled with the 3 enemy prefabs I put in the editor, which it randomly selects from.

Attached to each of the 3 enemy object prefabs, I have a "Enemy Projectile" script which moves the enemy object down and reloads the scene if it collides with the player (resetting the game):

Code (CSharp):

1. private void FixedUpdate()
2.     {
3.         transform.Translate(Vector3.down * enemyProjectileSpeed * Time.deltaTime);
4.     }
5.  
6.     private void OnTriggerEnter2D(Collider2D collision)
7.     {
8.         if (collision.CompareTag("Player"))
9.         {
10.             SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
11.         }
12.     }

Now, attached to my Player object, I have a script which detects input from the user and then shoots out 1 of 3 prefab'd bullets, when either A, S, or D is pressed.

Code:

Code (CSharp):

1. private void PlayerShoot()
2.              if (Input.GetKeyDown(KeyCode.A))
3.             {
4.                 Instantiate(projectiles[0], new Vector2(transform.position.x, transform.position.y + 0.6f), Quaternion.identity);
5.             }
6.             else if (Input.GetKeyDown(KeyCode.S))
7.             {
8.                 Instantiate(projectiles[1], new Vector2(transform.position.x, transform.position.y + 0.6f), Quaternion.identity);
9.             }
10.             else if (Input.GetKeyDown(KeyCode.D))
11.             {
12.                 Instantiate(projectiles[2], new Vector2(transform.position.x, transform.position.y + 0.6f), Quaternion.identity);
13.             }
14.         }
15.        

Each of the projectiles the player shoots is chosen from a list of 3 prefab'd bullets and each of these bullet prefabs has a script attached, called "Projectile Script". In this script, the bullet is moved upward starting from the player's position, and destroys the enemy projectile if it collides with it.


The problem I am having is figuring out how to detect collision between those prefab'd objects I instantiated during runtime. The projectiles my player is shooting, and the projectiles falling from the sky. I can use the OnTriggerEnter2D() method inside the player's bullet objects' scripts to detect collision between itself and an enemy through tag searching, but cannot figure out how to add a reference to anobject outside of the prefab itself.

I'm trying to get a UI Text object which displays my score in the top left of my screen to go up every time one of my bullets collide, but cannot figure out how to make a reference to it and change its text in the projectile prefab's code. I also can't figure out a way to detect the collision between the objects outside of the prefabs, like in some other script.

I hope what I asked makes sense! Thank you!

 

For reference, I decided to model my game after Blackthornprod's "MAKING A GAME IN 10 MINUTES IN UNITY - BRACKEYS CHALLENGE !" video, link to video so you can see what my project sorta-looks like (11:55 shows the end result):