Lost the UEFI boot info that my BIOS shows

[Fulko Hew]

Something went wonkers with my system, and although I could try to reboot
it would get so far and then fall back into some kind of maintenance mode.

Rather than fight it at the time, I thought it was a good time
to ensure I have a good backup of my home filesystem.
So I booted a Live USB stick and performed my backup.

Now I wanted to go back and try to diagnose/fix my root filesystem issue.

Sadly, my BIOS no longer knows about the bootable entity on the HD,
and only shows me the Flash drive (even if it's not plugged in).

Any idea what happened to my HD boot info in my BIOS, or how to restore it?
PS. It is a Dell laptop.

TIA
Fulko