a quick google search for this term:   how to recover a bricked rx580 flash

brought up this top result: https://www.techpowerup.com/forums/threads/i-bricked-my-msi-rx580-gaming-x-gpu-but-not-anymore.234724/

check for more if it doesnt work, but this looks like it may help you.

Step one;  get an original copy of your BIOS (you backed it up before flashing riiiiight???)