Installation of an alternative OS?

How can I access NitroWall BIOS to install a new OS?

HDMI doesn‘t seem to work - Cannot access BIOS to select a USB drive to boot from.

Don’t have a Nitro Wall however I experience the same with other mini PCs. I need to try out different HDMI cables and then it suddenly works. Also have a cheap 9€ HDMI to USB grabber card for that purposes. Then I can use a laptop as display and this usually shows UEFI BIOS quite well.

I guess the Monitor negotiates screen resolution and HDMI capabilities and is not fast enough or does not allow the required settings and the display stays blank.