Can’t boot (boot points to missjng or corrupt legacy BIOS?)

Is it possible to change boot method from legacy to UEFI without going through f2 setup?

I have a Aspire E1-470p. I had upgraded it through Win10 but it was running slowly. I decided to try Ubuntu. I created a Dual boot (Ubuntu/Win10) and it worked well.
The good news is my PC ran like new. The bad news is that in the repartitioning I may have deleted or corrupted my Legacy BIOS without knowing it. However still using UEFI I was unaware of this.
Fast forward to last night. I wanted to expand my Ubuntu partition. I created a Ubuntu Live thumb drive. However it would not boot from it even when I changed the boot order.
Monkeying with the setup I think I switched from UEFI to Legacy (which may not exist.) and I may have changed secure boot as well. I am not positive.
Now when I try to boot I get “no operating system found”. If I boot using the Ubuntu Live (works sometime not other times) I can see the partitions but I cannot use Ubuntu Boot-Repair which wants an EFI session.
F2 at startup
Is there a way to manually change back to UEFI to get back to my dual boot?

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Pallama

Sorry. F2 at boot does nothing. No setup screen.

johnjtraynor

Resolved.

I could not get into firmware. I think Ubuntu was in Legacy BIOS mode and wouldn't let me get back to UEFI.

I removed battery, opened the laptop, removed the CMOS battery and HDD, replaced the CMOS, put in battery, booted (Operating System not found), powered off, reattached the HDD and booted again and voila back into Windows 10 UEFI.

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