i hate to ressurrect topic but
maybe it will help fellow googlers
https://www.techpowerup.com/download/ati-atiflash/
techpowerups UEFI Shell Version allowed me to flash bricked card.
in windows version no matter what i did, "error reading from ROM" was the message.
i can't recall the exact syntax
amdvbflash -p 0 romname.rom
if i recall correctly.