Rotating player with Quaternion and RotateTowards

My 3D character is a Cow and can be pushed away by a collision, in which i'll apply a Force and Torque so that the character can be knocked back approprially. When the character enters collision, it goes into a 'Ball' position, in which it just rolls around like a ball. This i'm achieving already. However, now I wanted to rotate the Cow in such way that it is able to transition into the normal/walkable position. For example if the Cow is in the Ball position, with its belly up, facing forward in the World, i just want to rotate around the Z axis so that the belly is facing down, and now I can transition into normal/walkable position. I am already rotating the player, but for some reason, after rotation, the character ends up always facing forward in world coordinates but that's not what I wanted. I want that, if the character is facing to the right with the belly up, it will still face that direction but with the belly down. How can i achieve this? I think im close but can't get there.

 private IEnumerator StandUp() {
         float yRot = rb.rotation.y;
         Quaternion targetRotation = Quaternion.Euler(0, yRot, 0);
         Vector3 direction = targetRotation * Vector3.forward;
         while (Vector3.Angle(transform.forward, direction) > 1) {
             rb.rotation = Quaternion.RotateTowards(rb.rotation, targetRotation, 8f);
             yield return new WaitForSeconds(0.00f);
         }
         { ... } // animator controller -> set normal/walking state
     }