The most convenient way to flash the BIOS through hardware is to plug, unplug or switch a jumper on the motherboard for switching jumper that connects the central pin and a side pin of a set of three pins, the one should unplug the jumper and then plug it to the central pin and to the pin on the reverse side. So if the jumper is generally on position 1-2  one has to put it on the position 2-3 or vice versa. This jumper is not always situated near the BIOS but could be anywhere on the motherboard.

To trace the perfect jumper a person should go through the motherboard's manual. Once he has identified the correct jumper, switch it (or plug or unplug it, depending from what the manual says) while the computer will be switched off. He has to wait for couple of seconds and then it will be better for him to place the jumper back to its original position. In some motherboards it may occur that the computer will automatically runs after the occurrence of the flashing of the BIOS. In this case it will be better to cut the power to it and place the jumper back to its original position. Next one must switch it on again. Other motherboards need you switch the computer on for a few seconds to flash the BIOS.

If one doesn't have the motherboard's manual,  it will be better for him to have to "brute force" it... trying out all the jumpers. In this case, one should first the separate ones (not in a group), the ones near to the BIOS, and the ones one can switch. If all them fail, one should try all the others. However, one must modify the status of only one jumper per attempt, otherwise one can do a lot of harm to  the motherboard .  If the password request screen is still active, one should try another one.