Hi Juliann. First I would make sure his sodium intake is in check. Try to decrease any processed foods that may have hidden sodium. This can help to keep water off the body and decrease swelling.
Adding foods that promote fluid excretion are very beneficial when it comes to swelling. Parsley, celery, asparagus and watermelon all have a diuretic effect on the body and can decrease water retention.
I hope this helps, keep me posted!