Based on https://www.franka-community.de/t/reset-admin-password-or-reset-to-factory-settings/184, there are two ways recommended by Franka Emika:
First way
1. Navigate to the login page of Desk.
2. Open the debug window.
3. Switch to the console tab.
4. Enter <fetch(“/admin/api/factory-reset”,{method: ‘POST’})>, without the <>.
5. Pressing enter does a factory reset. Just wait for the reboot (robot will start blinking in yellow).
Second way
Manually boot the controller into the Rescue System, by performing the following steps:
Shut down the controller and switch off the main switch as soon as the fans are switched off.
Wait approx. 10 sec. Before restarting the control by switching on the main switch.
Wait at least 20 sec and less than 40 sec.
Switch off the control unit with the main switch.
Wait 10 sec.
Start the control again by switching on the main switch.