SSH to your Unifi radio
ssh to ubnt:192.168.1.20 (or whatever the IP address is.)
default password is ubnt, if it something else, I hope you wrote it down when you set it. :)
Reset to defaults
You must reset the AP to defaults before changing the inform ip address.
This will reboot the radio and disconnect your SSH session. Once it comes back online, you will need to reconnect.
Set new inform IP address
Connect to the mca client
Now issue the set-inform command with the IP address of your Unifi controller.
The AP should connect to the controller within a few seconds and you are set.