For RX 500 Series (Polaris) and Older:
Get amdvbflash 2.93
https://www.techpowerup.com/download/ati-atiflash/
Then look for Version 4.68, underneath 4.68 you will see a link to show older version, click that and you should see version 2.93
Follow these steps carefully:
1. Open your "C:" drive in Windows, create a new folder, call it atiflash.
2. Extract the contents of atiflash_293.zip to the "C:\atiflash" folder
3. Find the bios file you downloaded and rename the bios file to 5 digits with .rom on end Example RX 580, change file to rx580.rom (r****.rom)
4. Move r****.rom to the "C:\atiflash" folder
5. Open the start menu, type cmd, when cmd.exe appears right click it and hit "Run as administrator"
6. At the command prompt type in cd\ and press enter until only C:\> is on the screen.
7. Type in cd/atiflash and press enter, you should see C:\atiflash>
8. Type in amdvbflash.exe -i to identify the gpu you want to flash with a 0, 1, or 2)
9. At the C:\atiflash> prompt type in
amdvbflash.exe -unlockrom 0
(there is a space between the e and -unlockrom and 0)(0 is the number zero)
press enter and you will be prompted that the "ROM Unlocked" (or 1, 2)
10. At the C:\atiflash> prompt type in
amdvbflash.exe -f -p 0 r****.rom
(there is a space between the .exe and -f, and a space between -f and -p and 0).
(Or 1, 2)
Press Enter
Follow directions on screen and if flash is successful exit the command prompt and restart, windows should show up on screen