When you want to locally SSH onto devices, there is a prompt to enter a username and password. If the device is in a factory reset state (solid orange or white LED on the unit), the username and password would simply be ubnt.
However, when the device is set up on a controller there will be a set username and password. To locate this information, you will need to go onto the settings page within the site they are allocated to on the controller > site > device authentication.
**PLEASE NOTE** If you want to change the device authentication username/password, it is not recommended to use an email address for the username.