What should I do about a cramp in my femoral artery?

See a physician. I assume you are having pain in your groin area. Arteries cannot have "cramps". Time to see a physician for an exam.
Femoral artery cramp. Complaint suggests discomfort in the thigh area, without significant more history or examination it is not possible to give meaningful advice.
Cramp in artery. In the artery one gets clots or dissection. When that occurs there is excruciating pain and if a clot the leg below the clot is cold/ numb and pulseless ,it is a medical emergency and go to ER immediately. A cramp in the muscle due to low potassium ,magnesium ,calcium ( or high calcium), exercise, autoimmune. Replenish electrolytes if low, epsom salt bath ,massage. F/U today with doc.