Connect to serial console with these settings : 19200-8-N-1.

Power cycle the ap.

While the AP is booting, hit the escape key.

You should be greeted with a boot> prompt.

Now, let’s return that thing to factory defaults :

boot> set factory_defaults
This operation restores the switch to the same state as it was in when
originally shipped from the factory.  All configurations, licenses, dumps,
keys, etc. will be deleted. Continue [y/n]:y

boot> reset

You should now be able to log into the web ui using https with the following credentials :

user : admin
pass : admin123

…and remember, if you have garbage on the console, chances are you’re not using the right driver : make sure it’s FTDI.