I believe that just about every sports athlete and fitness guru has run into this problem. I've addressed already what to do to prevent chaffing, but let's say that we didn't follow that. What are some things that can be done to treat chafing?
I have found that using Desitin or other 'diaper rash' ointments helps to relieve the pain and swelling. Apply to the affected area liberally and rub it in. I suggest an application of twice daily.
WARNING: these rash ointments do have active ingredients and therefore make sure you are not allergic and discontinue use if skin gets worse. Be sure to follow the directions precisely.
You for sure want to make sure that your skin stops rubbing against the material that has caused the chaf.