When you can, trim the feathers from around the wound. Then take a better photo of the wound with good lighting and a plain background behind your hen so your camera will focus on the wound.
Do you have any oral antibiotics on hand? You won't be able to buy them in Calif. without a vet prescription. But people antibiotics will work fine. Let us know what and the strength and we can calculate dosage.
Is the hen in a weak state? Or is she active and eating and drinking? If she's weak, give her sugar water, a teaspoon to a cup, and try to get her to drink it. It will elevate her glucose and stabilize her chemistry.
Here is my wound care protocol:
1. Treat for shock as the number one step. Give warm Gatoraid or mix a half teaspoon of sugar into a fourth of a cup of warm water with a pinch of salt and baking soda. Have the patient drink it all or syringe it into the beak.
2. Flush the wound well with saline. This is better than soap and water as it maintains the PH of the tissues. But warm soap and water will do. You need to wash away the bacteria from the wound.
3. Inspect the wound carefully. If it has a skin flap dangling, keep that. Do not cut it off. Look for bite, tear or puncture marks indicating a puncture wound. If you see this, the patient will need an oral antibiotic such as amoxicillin. Bacteria from the predator’s mouth can be injected deep into tissue and can kill in as little as 24 to 48 hours. You can order this
https://www.kvsupply.com/item/aqua-mox-250mg-capsules-100-count/P06184/250mg once a day for ten days. Or you may be able to find this or something similar at TSC or a pet store.
4. Spray with Vetericyn wound treament and let dry. Use a topical antibiotic ointment such as Neosporin or a generic without pain killer in it to coat the wound. If there's a skin flap, lay it across the wound that has just been coated with the ointment. Then smooth on a generous amount over the top of the skin flap to hold it in place.
5. It's useless to try to stitch a wound on a chicken. Don't even try. It's also useless to try to bandage a wound other than on the feet. The chicken will not tolerate it. It will be pulled off faster than you can blink an eye.
6. Clean the wound every day following the above steps. Keep the wound covered with the ointment. Never allow the wound to get dried out or it will not heal.
In your photos you've posted, it appears some of the tissue around the wound is dying off, necrosis. You will need to gather your hormones and put your tough girl suit on because this is going to hurt. It may also be a little painful for your hen.
You need to debride the wound. Under the black stuff is bacteria. The black stuff has to be scrubbed off. Completely off. Use soap in warm water and a wash cloth. When all the black crust is gone, rinse with saline and proceed with step #4 and dress the wound.