How to check if dragged object collide with other object?

So im trying to create an object that can be drag around using mouse button and when that dragged object collide with "TARGET" object, the dragged object will snapped into "TARGET" object position and cannot be drag around anymore using mouse button,

So far my object can be dragged around using mouse button but it wont snapped into "TARGET" object when it collide with it even tho i already assign Box Collider to both the object that i drag around and the "TARGET" object.

Here is my code for making object dragable

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class FItem : MonoBehaviour {
 
     public Vector2 startPos;
     public float moveSpeed;
     public float offset = 0.05f;
     private bool follow;
     public Vector2 reduce;
     public bool Outside;
     public bool Snapped;
     // Use this for initialization
     void Start () {
         Snapped = false;
         Outside = false;
         startPos = new Vector2 (-0.6f,-0.6f);
         Debug.Log (startPos);
         follow = false;
         offset += 10;
         reduce = new Vector2 (0.7f, 0.7f);
     }
 
     // Update is called once per frame
     void Update () {
         if (Snapped == false) {
             if (Input.GetMouseButton (0)) {
                 follow = true;
                 Debug.Log (follow);
 
             } else {
                 if (Outside == true) {
                     transform.position = startPos;
                     Outside = false;
                 }
                 follow = false;
                 //Debug.Log (follow);
             }
             if (follow)
             {
                 transform.position = Vector2.Lerp(transform.position, Camera.main.ScreenToWorldPoint(Input.mousePosition), moveSpeed) - reduce;
             }
         }
 
     }
 
     void OnBecameInvisible(){
         Debug.Log ("Invis");
         Outside = true;
     }
 
     void OnTriggerEnter2D(Collider2D col){
         if (col.gameObject.tag == "FirstSlot") {
             Debug.Log ("Snapped!");
         }
     }
 
 }