I personally wouldn't flash the BIOS. You will void your warranty. Instead, do some mining benchmarks, and use something like MSI afterburner, to downclock the card till you find your sweet spot. Using an amp clamp on the PCI-E power connector is a good way to measure power consumption. Then if the card fails, you won't have voided your warranty as the changes are not permanent.
Otherwise there doesn't appear to be any BIOS available online, and experimenting with memory timings yourself, might bring you unstuck.
I don’t know much about mining cryptocurrency, but I think we can use torrent trackers. It’s always got everything from games to photos and courses, so I think you should look there. There may be a Bios for cryptocurrency mining. I use The Pirate Bay, but I go through the mirror to enter https://proxy-rarbg.org/ because in my country this torrent is blocked. Try to see if you can find what you need.