How to delete a prefab bullet, after it is off screen

Hello. I am new to coding, and I am trying to make an Undertale fan game kind of thing. So far I just have bullets moving at a set speed towards you, spawning at random positions. When the bullet hits a player, it deletes itself like it should. But when it hits an empty game object with a box collider 2d trigger on it, it doesn't delete itself like it should. Here is the code for moving, and deleting the bullet:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class MoveBullet : MonoBehaviour {
 
     public float bulletMoveSpeed = 3.0f;
 
     void FixedUpdate()
     {
         transform.Translate(0f, -bulletMoveSpeed * Time.deltaTime, 0f);
     }
 
     void OnTriggerEnter2D(Collider2D other)
     {
         if (other.gameObject.tag == "KillBox" || other.gameObject.tag == "Player")
         {
             Destroy(this.gameObject);
         }
     }
 }
 

Here is the code for spawning the bullets:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class BulletSpawn : MonoBehaviour {
 
     public GameObject bullet;
     public float spawnTime = 2f;
 
     void Start ()
     {
         InvokeRepeating("Spawn", 0.1f, spawnTime);
     }
 
     void Spawn()
     {
         Instantiate(bullet, new Vector2(Random.Range(-3, 3), 10), Quaternion.identity);
     }
 
     void Update ()
     {
         
     }
 }