Change input direction to camera's forward

This is basic vector math but somehow I'm still stuck after 2-3 hours :(

I have this camera which is controlled by touch inputs, 1 finger is moving (when you swipe left, the camera goes right, so the whole scene should go left), 2 fingers is rotating (this works).

But when the camera is rotated, the 1 touch swipe is still in world space (or something), It has to react to the camera's forward direction.

                 if (touch.phase == TouchPhase.Began)
                 {
                     startInput = touch.position;
                 }
                 if (touch.phase == TouchPhase.Moved)
                 {
                     //1 finger down to move screen
                     if (Input.touchCount < 2)
                     {
                         targetPos = transform.parent.position + new Vector3(startInput.x - touch.position.x, 0, startInput.y - touch.position.y);
                     }
                 }
             

This is in the update:

     transform.parent.localPosition = Vector3.Slerp(transform.parent.localPosition, targetPos, 4 * Time.deltaTime);
     transform.parent.rotation = Quaternion.Slerp(transform.parent.rotation, targetRot, 4 * Time.deltaTime);

Any idea what I have to multiple/add/substract from the basic input in order to get the same movement even when the camera's rotated?