How develop reaction when object colllide with another

Well if i understand ur question correctly u should make a box collider so u can trigger a script that moves ur character back from that position. So basically ull need a cube that has a box collider and the check box for is trigger is checked. Then ull need to make a script that entails the following code(c# is what i use)

 using UnityEngine;
 using System.Collections;
 
 public class cameraTransistion : MonoBehaviour {
 private Transform currentTarget = null;
 public Transform player;
 
 void OnTriggerEnter(Collider col)
     {
         if(col.tag == "trigger")
         {
             
             currentTarget = col.transform;
             Debug.Log("Enter");
         }
         }
 
 void Update () {
         if(currentTarget != null)
         {
               player.Translate(1f,1f,1f);
                 currentTarget = null;
         }

}

now that should work and u can alter it to ur liking but thats base logic