You can factory reset an access point, switch or USG by depressing the small reset button with a paperclip on the back of the device. You will need to hold in the button until the LED light goes off.
Once the reset has completed, the LED light will show as solid white/orange (depending on your model).
*PLEASE NOTE* Depending on the model you have, the reset button location will vary and can be confirmed within the Quick Start Guide that comes within the box. Alternatively, you can download the guide through Ubiquiti's website https://www.ubnt.com/download/unifi/ for more information.