I think the only thing you can do is maybe rinse with saline....or if you have chlorhexadine. But, definitely get him to the vet in am.
It could be one of these ( I don't really think so, but worth thinking about)..... but could also be so many things. Definitely looks "angry" and might be a cellulitis secondary to a bite or something.
https://www.merckvetmanual.com/integ...-dogs-and-cats