I was bitten on the penis 3 weeks ago. The inflammation/bite marks have not completely disappeared. Will it heal? Anything I can do to help healing?

Probably will heal. "Not completely disappeared" implies it is quite a bit better than it was. Healing probably will continue to improve until complete. Human bites can cause difficult to treat infections, so see your doctor if it has stopped improving or is getting worse, or if you remain in doubt.
Depends. The answer to your question may be related to what bit you as well as how deep and wide of an area the bite created.