How to check for a collision between 2 colliding prefabs?

How to check if two objects are colliding separate from the object the script is attached to?

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

public class collidingObjectScript : MonoBehaviour
{

public Slider slide;

void OnTriggerEnter(Collider col)
{
    if(col.gameObject.tag == "Missile" && col.gameObject.tag == "BossMeteor")
    {
        slide.value -= 1;
    }
}

}

Make the objects check for the collision by themselves and when they collide, call a function that decreases the slider value. I think its better like that.