You need to follow the steps described here. See the part about git credential manager or setting up ssh authentication. Make sure also that you have Git installed.
I used this a while back to setup git hooks, which are very handy for push, pull, commit, etc with a remote repository on GitHub. I don't think it's necessary to do steps 1 - 3 (Git Hooks) if you're just trying to sort out the credentials, but if you're working with remote repos regularly then it's pretty useful to have Git Hooks as well.
