What can I use to help relax the muscles in the knee area so I can complete therapy?

Relaxation technique. If you are in pain, you may need to use medication such as tylenol, (acetaminophen) ibuprofen, Naproxen etc. Occasionally, a muscle relaxor, such as flexeril/robaxin might come in handy, but due to strong sedative effect, i would not take them during the day. Heat applications, topical rubs (bengay, icyhot) may help in that. Light massage might be helpful as well.