The first thing to do is decide if you actually care. I try to do open source work so other people don't have to work as hard to redo what I did. If someone else wants to claim my work as theirs, it's annoying, but it doesn't prevent me from using my work and it may result in my work being more widely spread, so I guess it's fine. But that's just like my opinion, man.

If it bothers you enough to take action, and you've waited a reasonable amount of time for the other person to respond, your options are probably international copyright lawsuits or DMCA requests. Lookup the github dmca procedure and make a request with the proper information and go where it takes you. Expect to be called out as unreasonable, but whatever.