The wound is clearly very infected and it's only natural the dog turns it away from you. Please don't try to touch it, it may provoke a (defensive) attack.
You also have to realize that the dog may not survive. If the tissue inside the wound dies off (called a necrosis), it cannot heal and must be surgically removed. It might already be too late to avoid a sepsis due to bacteria from the infection spreading through the whole body.
To fight the infection and relieve the pain, I suggest you go to a pharmacy and ask specifically for one of these drugs:
- carprofen (Novox or Rimadyl)
- deracoxib (Deramaxx)
- firocoxib (Previcox)
- meloxicam (Metacam)
All of them are anti-inflammatory drugs and listed as safe for dogs by WebMD. Using human medication like ibuprofen or aspirin can lead to kidney failure in pets.
The pharmacists may ask why you need those (at least they should if they do their job right). Show them the pictures you've taken and let them estimate the proper dosage of the pills.
Give the dog the proper dosage twice a day (or according to what the pharmacist and packaging say) and always together with food. The stomach should not be empty when taking the pills. If the dog doesn't like the pills, coat them in something tasty like cream cheese or a soft sausage. Continue the treatment for as long as the packaging says it's safe.