Rotate a gameobject by a specific angle and stop when character doesnt move anymore

So basically what I am trying to do is when I move my character via joystick I want to calculate the current angle the character is rotating and the new angle in which he should rotate. for example: i am currently moving at 45 degrees. now I move the joystick to 90 degrees. So basically I want to calculate the difference between the current and new angle and than rotate at that specific angle. In this case it would be 45 to left.

Here is where I calculate the new degree:

 void Update()
     {
         // move
         _rigidbody.MovePosition(transform.position + (transform.forward * leftController.GetTouchPosition.y * Time.deltaTime * speedMovements) +
             (transform.right * leftController.GetTouchPosition.x * Time.deltaTime * speedMovements) );
 
         if (myX != leftController.GetTouchPosition.x || myY != leftController.GetTouchPosition.y) { //checks if player changed position.
             myX = leftController.GetTouchPosition.x;
             myY = leftController.GetTouchPosition.y;
 
             double rad = Mathf.Atan2(leftController.GetTouchPosition.y, leftController.GetTouchPosition.x); // In radians
             double deg = rad * (180 / System.Math.PI); // values from up right to up left : +0 to +180 and from down left to down right: -180 to -0
 
         //    double difference =....;
         //    transform.Rotate(Vector3.up,(float)difference * Time.deltaTime);
 
         }
     }