The spring to keep close a hunter case serves in this case also to unlock the hand setting.
In a cutout works such a spring fixed by a screw. The tube which is pushed over the stem is exactly so long that it touches the spring face. The tube remains movable from the spring to the push button.

Note, the bezel of the inner crystal covers over the spring nose, but the nose must be able to move.

If one pushes the crown button, the tube pushes against and moves the spring nose back. The front cover jumps up. Hand setting is possible. Is that done and one close the cover thereby the rim of the cover pushes the spring nose back which attacts then a special lever of the hand setting at the inner of the movement and looses the catch. Use this Link for a clip demonstration!

The lever of the hand setting is too short, a new one is made.