Sites that may help you find the magic key:
https://www.fsf.org/working-together/moving/bios-howto
Due to the archaic nature of BIOS set up screens, this is a potentially tricky task, and where possible, we recommend you contact your local LibrePlanet group, friendly local computer store, or perhaps a friend or relative who is good with computers to help you.
https://libreplanet.org/wiki/Main_Page
https://www.computerhope.com/issues/ch000192.htm
This is one of the most comprehensive before you start some serious googling.
Google: Access the BIOS on ACER 5755G
or
Youtub: Access BIOS ACER 5755G
https://www.lifewire.com/bios-setup-utility-access-keys-for-popular-computer-systems-2624463
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