Unplug the unit. Remove he three screws along the top back of the control panel and set them aside. Locate the timer, and carefully twist the body to remove the metal stays from the inserts on the control panel.
Carefully remove each wire form the old switch and connect it to the new switch one-by-one, following the lettered codes on each terminal. When all wires have been installed on the new switch, install the switch using the metal tabs onto the backside of the control panel.