FortiNAC-CA-700F, boot device lost after trying to upgrade firmware

Hi all,

I and my colleagues have tried to upgrade a FortNAC-CA-700F appliance to a newer firmwar by following this guide https://docs.fortinet.com/document/fortinac-f/7.2.3/release-notes/195805/system-update-settings

After reseting the appliance to factory default we are presented this screen:

If we press 'DEL' nothing happens, though if we press 'TAB' we get shown this and are required to enter a password (and we actually don't know which passwordto enter):

Else, if no button is pressed, then this is shown:

Not sure how to preceed.

Can anybody help with this?

Thanks