Hello!
If you're curious about migrating repository to GitHub from GitLab or another registry I've recorded a quick demo on that.
I've found 2 possible ways to do that, but only one of them supports both public and private repositories. GitHub has the import functionality available in UI, but unfortunately, it seems not supporting private repositories so far. Anyway, it's a very easy task to do. Take a look at the video, just 2 minutes...

Thanks for watching! And please let me know if I've missed something here...