What are you hoping to gain by flashing your RX 580 card BIOS?
Is the card non-functional and you hope to restore it to operating condition?
Do you have an OC BIOS that you want to flash to attain higher clock speeds?
Are you trying to flash a different model card BIOS to unlock cores/shaders?
Go to TechPowerUp to download AMDVBFlash (previously known as ATIFlash) which has been around forever. You will need to make a bootable media to run the flash utility from. Also highly recommend you have backup graphics (such as IGP) to run from while flashing.
https://www.techpowerup.com/download/ati-atiflash/
BE AWARE YOU CAN BRICK YOUR CARD DOING THIS.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT