Just put a few drops of povidone iodine (same red stuff they use to clean wounds and prep for surgery) in the water, just enough to give it a little color. make sure the water temperature is close to the same temperature as the snake. Try to keep the snake's head away from the solution and try to get the body to soak in the liquid for as long as you can, up to 10 minutes. This is only necessary if there is actually broken skin or fluid-filled blisters, punctures, or other injuries and will help get rid of, or prevent infection. Not really necessary if all that's wrong is bent back scales but anyway, it can't hurt. Just don't poison the little guy. Rinse thoroughly and keep it away from his mouth and nose. If the neck is kinked it probably won't help with that. Sounds like a spinal injury. Many snakes go on to live full lives, even with kinked broken spines. If you have trouble soaking him you could probably get idodine swabs or pads and/or apply the iodine with a cotton ball, leave it on for a minute, then rinse.

If he seems fairly alert and there is tongue flicking going on, he's probably going to be fine as long as he doesn't get an infection. I've seen massive blood loss, exposed ribs, broken spines, etc. from lawn mowers and they survived.