How do I do a BIOS recovery on an Acer Aspire ES1-531-C3X2?

Yes, that is worst thing that can go wrong, unplug the power adapter when BIOS is flashing. I recommend that you do bring your laptop to Acer Services in your country as your laptop is "bricked", and the EEPROM needs to be reprogrammed or often they just replace it, charges won't be much.
You can try to reset the CMOS coin battery located on the right side of the main battery: Open the back of the laptop and find the small round plastic capsule the size of a coin, open it, take out the small battery and shorten the +/- contacts inside the capsule with a bended paperclip for a second, put the battery back in the original position and close the capsule and back of the laptop, try if the laptop will boot.
Attempting to flash BIOS downloaded on another PC with a USB stick won't work 80% of the time, but if you don't mind the frustrations when it fails, here is how you can try it:
Format a USB flash drive as FAT32.
Download the latest version of the BIOS from Acer support website:
You will have to enter your model number to get the correct version for your Acer laptop.
Extract the files from the zip and put both the FLASHIT.EXE and the BIOS file in the root directory of the USB flash drive. Note, Acer BIOS versions contain different .exe file names, for the Nitro that is H2O*.exe
Rename the BIOS file to ZG5IA32.FD and then remove the disk.
Turn the laptop off, insert the battery and connect the AC adapter.
Insert the USB Memory Stick into one of the USB port of the Aspire laptop.
Press Fn+Esc, keep it pressed and press the power button to turn the laptop on.
Release Fn+Esc after a few seconds, the power button will be blinking.
Press the power button once. The laptop will start the BIOS flash, do not interrupt for any reason. After some minutes the power button will stop blinking, and then the laptop will reboot. Wait till it has completed all these operations. This may take 30 minutes or more.