To program a new button in, you'll need to know which transmitter slots are in use and which you want to program. The below instructions will program the transmitter into slot 1.
Programming steps:
1) Remove the cover from Add-On Receiver
2) On the Add-On receiver, press the Advance button to select the transmitter slot to program
3) Press the Program button to move to the next configuration setting (Supervision Window/Sup Wind)
4) Press the Advance button until light 1 (None) is lit.
5) Press the Program button to move to the next configuration setting (Output)
6) Press the Advance button until light 1 (output 1) is lit.
7) Press the Program button to move to the next configuration setting (Output Type/Out Type)
8) Press the Advance button until light 1 (Follow) is lit.
9) Press the Program button to move to the next configuration setting (All lights lit)
10) Press the Reset button on the device you are learning in. All the lights will turn off.
Everything should be programmed at this point and should work properly for you.
Attached is the manual for the Four-Zone Add-On Receiver.