Did not work with my 3700X + B450 I, Tried to downgrade from 2703 to 2501. Follow all the steps exactly. Error message was something like "string could not be loaded". Sigh.
and you renamed the bios file you wanted to flash to bios.rom?
follow the steps in the video and don't be sloppy, the tutorial is very easy to understand
Extract and rename the bios you want to flash
Format the USB drive using Rufus, and replace the files on the USB drive, with the files from the ZIP + the extracted bios.rom
It should look like this, then reboot, enter bios and select boot overide, boot from USB drive (non UEFI), then it will automatically update the bios