If it is an abscess, warm wet compresses will help and may help it drain.
How do you know it's an abscess? Is it draining or painful and soft, or ....?
You could also give him a baby/heartsmart 81 mg aspirin if he weighs about 10 pounds or 1/2 a tab if he is closer to 5 pounds. The generally suggested dose is 5-15 mg/lb 2-3 times a day. This can be repeated twice a day. The most common side effect is vomiting and this often occurs in the same range as the effective dose. If he starts, cut the dose in half or stop.
Do not use Tylenol, Alleve, Motrin/Advil or other OTC pain meds.
Let me know if you have follow up questions. I will be online for a bit longer and then go offline for the night. I'm on the east coast of US.
Witch hazel may sting a bit. If you have triple antibiotic or neosporin ointment, a bit of that might help.
Hopefully, the warm packs and aspirin will make him feel better.