How do I create a bootable bios flash drive

You download the motherboard bios from the manufacturer's webside and put the file onto a flash drive. In mobo's bios in my case I go to advanced options and it gives me an option to update bios from either the internet or I can choose a file. You click a file and it should automatically detect the file on the flash drive you just have to confirm its on that flash drive and then dont unplug the pc...follow the on screen instuctions and wait for it to update and restart