How edit transform.forward value ?

Hi, i want to set the value of transform.forward the Z axis value of object hit by raycast to make something like that for exemple :

Here's my code

 private void Update()
 {    
     RaycastHit hit;  
 
     transform.Rotate(Vector3.up * mouse_h);
          
     if(Physics.Raycast(transform.position,-transform.up, out hit, 10000f)){  
 
 
        
         transform.forward = XXX;
 
 
 
         print($"hit : {hit.transform.name}");
     }
 
     Debug.DrawRay(transform.position,-transform.up * 500,Color.red);    
 }
 
  }