You are doing it wrong, I've been warned several times to never have another GPU on board when you plan to flash bios because the app can be confused and you will end up bricking the GPUs, so do it one after the other, insert Just one GPU in your motherboard and flash it, repeat this process to be on safer side
Read the information about sewing the BIOS of a video card using hive OS or other Linux systems.
To do this, you only need PolarisBiosEditor, and the procedures for downloading the BIOS and firmware of the video card are conveniently done with the help of the Hive OS graphical interface.
Hive Os numbers the BIOS files of video cards according to the numbers on the dashboard so that you don't confuse them.