How do I get into the BIOS in Linux?

Power off the system. Power the system on and quickly press the “F2” button until you see the BIOS setting menu.

How do I boot to BIOS in Ubuntu?

Ordinarily, to get into BIOS, immediately following physically switching the machine on, you need to press the F2 button repeatedly (not via a single continuous single press) until the bios appears. If that does not work, you should press the ESC key repeatedly instead. Have you done the above?