try this procedure captured from the net
- Open a command line, as administrator, and browse to the Atiflash folder. Type atiflash -i to list the GPU or GPUs you have connected. Once the first one will be "0", then 1,2 and so on if you have more than 1 connected.
- If you are comfortable with the GPUs that are connected, you can now flash the BIOS by typing "atiflash -f -p 0 BIOS.rom" without the quotes, where "0" is the number of the GPU you want to flash and "BIOS.rom" is the name of the ROM you want to flash to the card. It will give you some info on what it is doing and then take a minute or 2 to flash. When it is done, it will prompt you to reboot to make the changes take effect
this is presumably you have already your modded bios in place
if not you may get follow this procedure
https://bitcointalk.org/index.php?topic=1954245.0