Expertise? What expertise?
Chop off foot. Cauterize wound. Wrap in clean bandages (i.e., woven plant fibers, animal skins, et cetera). Change bandages daily. Give the patient a peg-leg or crutch when he is well enough to stand. No need for a medical degree or alien intervention.
You can skip the first step if the foot was bitten off by a wild animal.
_________________
No love for Hamas, Hezbollah, Iranian Leadership, Islamic Jihad, other Islamic terrorist groups, OR their supporters and sympathizers.