I contacted Apogee about this problem. They said, "That is not
a user-serviceable part." They wanted me to send it back for
service. It didn't look so complicated to me so I decided to
take a look for myself.
To open the unit, you first have to remove the endcaps which
are held on with three Philips screws.
Then remove the rubber pads on the bottom. They are held on
with two screws and double-sided sticky tape. After that, you
can slide the bottom cover off.
Opening the case reveals three printed circuit boards.
Remove three Philips screws on the back of the unit to free
the main circuit board.
You can now access the upper button circuit board.
I started to remove the Philips screws only to find that the
circuit board was still held on to the nuts. I replaced the
screws and removed the two nuts to the switch cover that
was installed backward.
I replaced the button cover in the correct orientation and put
everything back together exactly as I took it apart.
Everything is correct now.