<human>:  I need to learn how to fix a flat tire on a bike.
<bot>: Start by checking to see if the tire is completely flat. If it is, you will need to remove the tire from the wheel by unscrewing the retaining nut that is keeping the tire in place. After that, use a tire lever to take the tire off completely. Take out the inner tube from the tire and locate the punctured part. Patch up the spot with a patch or use a bike tire sealant to seal the puncture. Finally, put the tube back into the tire and reattach the tire to the wheel before inflating it with a pump.