SSH into the UniFi. Note that the UniFi username and password get updated from the controller. Refer to here to find username and password.

ssh ubnt@192.168.1.20

run the syswrapper.sh script with the restore-default option

syswrapper.sh restore-default

Once the device is reset, log in over ssh and reconfigure.

Note that the username and password will now be ubnt/ubnt