Because Fast Boot doesn't enable USB controllers right away on boot, you won't be able to enter the BIOS via the typical keyboard shortcuts like F10/F12/Del. The solutions are to reset the CMOS by removing the battery for 10 seconds, using a PS/2 keyboard(if you still have them or even the ports) or setting the jumper for the same according to your motherboard.
Thankfully instead of the above you can simply type the following to enter the BIOS via ubuntu, windows users have another shortcut of pressing shift & clicking the reboot button or something(google it).
systemctl reboot --firmware-setup