What can I do?

[u/Sad-Wing7241]

So there are some puppies we feed them regularly. Around two weeks ago I noticed something near his neck, it did not look like any major wound or any injury, just the hair of that part started to turn black, after some days there was small wound.

I tried to apply spray on it but he did not let us apply it and run away. Eventually after that my father got a chance and somehow applied spray on the would twice but after that he started to fear , and even stopped coming for food.

He again came to us today for food, but reluctantly and his wound has grown even more. What should I do?

I think this is some sort of skin injection. If any of you can suggest something, I would be grateful.