Is this the same chicken that you made another thread about, saying something smells dead on/in it?
I think you're describing a cyst, which could be necrotic or gangrenous. Pictures would help.
What you need to do with the cyst, if indeed it is a cyst, depends on what sort it is and what caused it and where it is... Either way, if you don't have something for lancing and disinfecting on hand, and possibly stitching, it might be an idea to have those items on hand just in case; also a vet visit may be worth considering if it's within your means.