Grasp wrist roller handle with both hands; over hand grip.
With left hand gripping handle, relax grip of right hand and slide grip in front of handle (by flexing wrist) and regrip. Relax grip of left hand and hyperextend right wrist. Repeat sequence with opposite hands, alternating back and forth until weight plate has raised up near hands. Lower weight steadily with opposite movement or loosen grip slightly to control descent of weight stack. Repeat.
Also see Lever Roller Wrist Flexion.