I don't understand how to get this working. When workibg properly, you rotate a wheel on the frontof the bathtub and the drain plug would rise to drain or fall to plug. Recently somehow it stopped rising and falling. I can't figureout how to reset it. I feel like I need to fiddle with the screws at the bottom somehow to get the length of the screw right, but I don't know. Can anyone clarify or give some advice.