Disconnect the Proline Lynx garage door unit's power cord from the wall outlet.
Remove the garage door opener’s cover with a Phillips-head screwdriver. Pull the cover off once the screws are out.
Examine the inside of the exposed unit for the distinctive white sprocket, which is centered on the gear at the opener’s top. The sprocket is held down by two or three screws, depending on the exact model. Remove each gear screw with the Phillips-head screwdriver. Take out the socket to access the gear beneath.
Use the end of a flat-head screwdriver to pry the clip on the limit switch on the right side of the unit upward. This removes the clip's hold on the gear.
Pull the gear out of the opener.
Slide the new gear into place.
Follow your disassembly procedure in reverse to reset the limit switch clip, screws and sprocket.