Hi, I am Dr. Peter and would like to help.
1- How long ago did this happen?
This is what you can do:
1- Apply cold compresses for 5-10 minutes 2-3 times a day.
2- Give him Benadryl 1 mg per pound body weight every 8-12 hours.
3- If you notice him having difficulty breathing have him checked by ER vet immediately.
4- If the swelling not better in 24-48 hours have him seen by your veterinarian.
If you have additional questions I will be glad to answer them.