Hi
With laptops the situation varies massively about locating cmos button cell
It may be soldered to motherboard , it may need dismantling to get to location
In other cases on some Dells it is hidden in the main battery bay and can be un plugged
I would see how to remove the sata hdd , this is usually much easier
( remove mains power and main battery before removing hdd
Wait until bios times out trying to find hdd
Then try getting into bios, change back to correct setting
was this uefi or legacy
Or sata or ide ata legacy setting?
Regards
Mike Barnes