Try giving him a pain relief, and also some teething gel. That should help to settle the pain a little.
Besides that, you can put a wet washcloth in the freezer. Then give that to him to chew on, it should cool down and soothe the area.
Offer him some home made teething biscuits. I made mine with plain sweet biscuits, spinach and cottage cheese mixed together, and baked until golden brown. My daughter loved them.
Get a 'mesh feeder' and give him slices of frozen apple, banana or mandarin in it. It will help cool down the area once again.