Like I said I'm no expert or a vet! so please disreguard my suggestion if it doesn't make sense to you or seems goofy. I would know a little more if I could poke on it!
If it is soft and mushy around the black part and the swelling is mushy I wouldn't soak it. I think I would want that to dry up and scab over to heal.
I wouldn't use heat on it either - it would cause even more swelling and pressure and could damage tissue. (I pulled a leg muscle once and couldn't walk at all and the doc said to never use heat without ice instantly following for that reason.)
If you wanted to go all out you could use a hot heating pad for 20 min and then an ice pack for 20 min. This gets circulation in and then ice moves fluids back out. But - I don't know how involved you are with your chicken. (I'm not that close with mine and the fight wouldn't be worth it.) It is important not to stress your chicken - it takes a lot out of them!
When the swelling goes down you could soak it to help heal it but not so long it losens the scab.
I have read you can make an epsom salt compress by saturating some water with epsoms salt until the salt stops disolving in the bottom of the jar and then putting gauze in the water and then wrapping the injury. - but since
I would want to keep this dry - I would soak the gauze and cook it in the oven on a very clean cookie sheet wiped down with alcohol all laid out and unwrapped at 250 until the guaze drys out and then wrap the leg in it. It would pull the weep out of the leg (if it's oozy) - but I wouldn't leave it on longer than a day or two so you don't salt burn the leg.
Just some ideas.
I hope it's getting better today!
