Oh, very hard is not a hernia then. If it’s not soft then probably don’t need to aspirate it. If it’s hard I would get a very sharp knife, preferably scalpel, and make a small cut in between the veins where the skin is stretched tight.
If you see yellow mush, kind of like paper mache, then it’s an abscess and that’s probably the best outcome. If you see virtually anything else (purple or red flesh, a lot of bleeding) then it’s a tumor that may or may not be cancerous and you won’t get anywhere without a vet.
Before cutting you need to get a sharp knife/scalpel, some betadine, a saline solution, lots of gauze, and a syringe. Trim or pluck surrounding feathers if they’re in the way and clean the area with betadine (but know this is not a sterile procedure at all and infection risk is very real). If it’s an abscess then you can squeeze the muck out or scrape it out if it’s very compacted. The cut will need to be at least an inch long to do this, this will be tricky because of all those veins there. Once you have most of the muck out then start flushing it with syringe and saline. I can’t say whether wrapping should be done without knowing what it will look like but I probably wouldn’t wrap it. Keep the chicken in a clean area and clean the area at least once a day with betadine. Antibiotics may need to be started if it gets hot, red, puffy, or excessively draining. If it’s an abscess I might start antibiotics anyway. Tylan 50 is at most feed stores, along with the other supplies.
If there’s no pus in there to get out, then you need to stop. If it starts bleeding a lot (a little is normal) then be prepared to hold gauze over it until you can get it under control. Also know that if it is a tumor, there is a risk of agrivating it by cutting into it like that, but it’s your call.
Hope that all makes sense, it’s very early here, I’m a little scatter brained still.