How can you make welts fade away, from rubberband snapping?

Stop snapping and.. Well, the obivious is stopping what is causing it, in your case, snapping with rubberband. Topical cortisone, calamnide, oral zyrtec/benadryl can help. You probably have dermatographia (writting on skin) in which light trauma/pressure to skin causes the hive to appear. Often, the search for the specific cause is illusive. If not better or worsen, call your doc. Good luck.