transform.localRotation = Quaternion.Euler(0, y, 0);

Quaternion rotation;

void Update()
{
      float y += (Input.GetAxisRaw("Mouse X"));
    
   if(transform.parent) {    
    transform.localRotation = Quaternion.Euler(0, y, 0);
   } else {
    transform.rotation = rotation * Quaternion.Euler(0, y, 0);
   }
}

void OnTriggerStay(Collider other)
{
       GameObject vr = other.gameObject;
       if (transform.parent==false)
           if (vr.GetComponent<OnTrigger>())
                transform.parent = vr .transform;
}

void OnTriggerExit(Collider other)
{
        GameObject vr = other.gameObject;
        if (vr.GetComponent<OnTrigger>()) {
      rotation = transform.parent.rotation;
            transform.parent = null;
    }
}