Underneath the ram (remove ram) is a jumper marked J3
short this out for a couple of seconds.

This will reset bios right back.

Boot and go straight to bios (F2) and set your options as needed there.

Eg date, time, drives,and any other options the bios needs to be able to boot the machine. When you have done make sure you SAVE then exit which will re-boot.

If you didnt mess any bios settings you should be back in business

https://www.fixya.com/support/t2785754-acer_aspire_3690_bios_reset