There are lot of used Graphic Card (GPU) are in market and they previously used for mining. Many of these cards are flashed with custom BIOS to reduce the maximum performance. These are reduced to increase the life and danger of high temperature of card that may dead the card.
Like if you have Sapphire Nitro+ Rx 580 and this card default MHz is 1411. But they might reduce the MHz to 1250. You can check the MHz from GPUz.
To flash the VBIOS to official then first download the ATI ATIFlash / AMD VBFlash. This program will help to select any BIOS and flash your graphic card.
Use same website and search for your stock VBIOS collection and download it.
Open ATIFLash folder and run as ambdvflash file. You should open this file as a Administrator.
Then open amdvbflashWin file and load your BIOS image and program.
AMD VBIOS Flash Tutorial Video
Some BIOS Flash Tips For Overclocking
Other tips are that you can flash your old graphic card like RX 480 to RX 580 VBIOS. If some game only run on RX 580 then you can flash your old card to RX 580 to run the game.
You should stress test your graphic card after the BIOS flash to check if temperature is going above the recommended temperature. Replace the thermal paste, open CPU casing or increase CPU fan to reduce the temperature.