Hello Albert,
It all depends on whether the AP is accessible via the ge 1 port or not.
If it is, then either SSH into it and run the "delete startup-config" command or use the discovery tool with reset. If using this utility, make sure you reboot the AP first. You are only able to reset it within 10 minutes of the AP being up and running.
If the ge 1 port is locked (i. e. AP not accessible via the ge port) then your only other option would be to reset it through the console port using baud rate 115200 and the reset/FactoryDefault log in credentials.
Regards,
Chris
Christoph S.