How to select an already placed 3D object in ARCore Unity?

Hello, I am experimenting with ARCore unity (HelloAR) for quite some time. The problem I'm experiencing is that I am not able to select a 3D object already placed in the real world using raycasting. I've tried the old method :

 void Update () {
 
             foreach (var touch in Input.touches) {
 
                 Shoot (touch.position);
 
             }
 
     }
 
 
     void Shoot(Vector2 screenPoint)
     {
 
         var ray = Camera.main.ScreenPointToRay (screenPoint);
         var hitInfo = new RaycastHit ();
         if (Physics.Raycast (ray, out hitInfo)) {
             hitInfo.rigidbody.AddForceAtPosition (ray.direction, hitInfo.point);
         }
 
     }

Note that although this does work as a simple mobile application. This does not work with Google HelloARExample (The one where we place andy robot on an horizontal plane).Is someone able to solve this issue? Please help me out...Thank you in advance!