When a computer first starts to bootup.
There is a small period of time when you can access the bios.
All computers use a specific keyboard F key to access bios options.
It is up to computer manufacture what keys are used.
Example:
F2 to access bios setup.
F8, F11, F9, etc... to access a boot device selection menu.
It always says to press a specific F key.
But a single press of the key usually will not make it do what is expected.
So, you press it multiple times hoping it will make it work.
Simple solution.
Press the F key and do not release it, keeping it pressed down.
When the screen pops up, that it is supposed to make visible.
Release the key.