Have what appears to be a large spider bite on lower jaw. What can I do to reduce swelling and take care of it?

See your doc. Some spider bites can cause significant tissue damage (necrosis) and possible secondary infections, thus you should have this evaluated by your doc for possible treatments. Since it is on your face, I would not wait too long. Good luck..
Ice, Benadryl, (diphenhydramine)arnica. Apply ice in the first 24-48 hours, the heat. Apply arnica (multiple brands available otc, can try traumeel). Benadryl (diphenhydramine) 25-50 mg will help with swelling and itching.