How can I make an object moving on its own bounce off walls

I'm trying to make an object, moving on its own, going one direction, to go the opposite direction when it collides with a wall. I have done some things, like making the walls I want the ball to bounce off of prefabs, but I am stuck on what I should do next.

Here is my code so far:

 using UnityEngine;
 using System.Collections;
 
 public class enemyControler : MonoBehaviour {
     
     public float speed;
 
     void Update ()
     {
         transform.Translate (transform.forward * speed * Time.deltaTime);
     }
 
     void OnTriggerEnter(Collider other)
     {
 
     }
 }