You cannot reset the bios on a video card,the only way to do it would be to flash the firmware of the card with the same installed bios revision of the firmware, not recommended as getting the wrong image will trash the card.
I think you are talking about resetting the bios of the motherboard, it can be done on most boards by opening the case of the computer and located next to the cmos battery is a jumper moving it from pins 1-2 to 2-3 will do a reset to factory bios settings once done replace the jumper back to pins 1-2.
weaselman: i have reflashed it with the same bios, i have fixed many issues, it's ok, but I have flashed it 3 times (I am wrong) after 3 times, screen is more then normally bright, and pictures are shows slowly, how to fix this issues, if you know?