Remove standard thumb rest.

Slide thumb rest body (1) off mounting plate (4).

Use existing screws & holes to attach mounting plate (4), using the top pair of screw holes.

Slide the body (1) over the mounting plate (4), always moving from top to bottom.

Adjust height to a comfortable position. Re-mount the plate (4) using a different pair of holes if needed.

Adjust the height of the hook (2) relative to the body using the vertically mounted allen head screws (3). To raise the hook loosen the upper screw, then tighten the lower screw.

To remove, slide the body (1) down and off the mounting plate (4).