You can do this (sometimes this saved me of bad situations)
Install Team Viewer in this rig (with your rx 580 installed), than make this app open with windows and make an account to have access to this PC when you turn on
Install teamviewer in another PC or smartphone (but is difficulty to deal in a small screen), then turn on your PC with this "bricked" card
You'll have full acess via remote desktop, with team viewer, flash your original bios to RX 5700XT, if this not work, try to make this with a downloaded bios, here you can find: https://www.techpowerup.com/vgabios/
Thnks!
I was able to boot up with onboard Graphics and this bricked card showed up.
I flashed back the stock bios successfully.