I had 3 hens with that. I was scared & had no idea what to do, but my vet would charge 45 dollars for the visit & a couple hundred more to fix it so I watched youtube videos.
Ur pic looks like it is fairly early. One of my birds was exactly like that. She Was Limping too.
After watching a billion videos, I placed her on a table with a towel over her head. My husband made sure she was breathing the whole time & kept her calm. I cleaned it really good with epsom & warm water, then I used an exacto knife to cut out the dark piece. Then I used Peroxide Several times, They foamed a lot & bled a bit too. After I was done, I applied melaluca oil, I'm sure any disinfectant or antibiotic cream would work. Then I put more oil on a piece of cotton, stuck the cotton on the wound & wrapped the foot.
I left it wrapped for 2 days, removed & it healed, no prob.
The 2 other hens were worse off & I had to clean it a couple times. 2 are completely healed & the 3rd looks much better. Hers was really infected though, it was huge!
I'very only been a chicken mom for about 2 yrs, so I'm not an expert. But this worked for me. I love my babies, theyre my pets & I couldn't bare seeing them suffer.
oh & fyi, if ur easily grossed out or tenderhearted, be warned. I had tears down my face the whole time I did the surgeries. But I'm glad I did it cuz the girls seem happier & funny thing, one of them was always really nervous around me cuz i got her when she was 2 already. She seems to trust me now despite hurting her. She doesn't run when I approach her
Hope any of this helps. Good luck!