Well as far as I know, depending on the motherboard manufacturer, you can flashback a bios on to the motherboard via a usb. You must check the said manufacturer site to see how to do it, but basically, you have a USB with the appropriate file system with the correct file, put it into the motherboard, which has to be plugged in, of course there is a USB port just for bios flashback so you have to check which one it is. Then final, you have to press the bios flashback button with the correct method for the bios flashback to occur.
Of course you need to read the manual for more detailed steps.