[SeaBIOS] accessing BIOS settings

[Chris 😶🙃😵]

Good day,

A have a Samsung Series 3 Chromebox on which I installed SeaBIOS (version 181214_15:29-johnlewis.ie) a few years ago.
I then installed Linux Mint, along with a GRUB.
I would like to know how to access the BIOS settings, i.e. which key or combination of keys do I press at boot time?
SeaBIOS displays "press ESC for boot menu" at boot time, but this just gives me the GRUB menu, not the BIOS settings.
The main reason that I need to access the BIOS settings is because it is not prioritising booting from USB over the hard drive (which is SSD).

Kind regards,

Chris