This is a copy from Jill Cates article How to update a forked repo with git rebase.
Step 1: Add the remote (original repo that you forked) and call it “upstream”
git remote add upstream https://github.com/original-repo/goes-here.git
Step 2: Fetch all branches of remote upstream
git fetch upstream
Step 3: Rewrite your master with upstream’s master using git rebase.
git rebase upstream/master
Step 4: Push your updates to master. You may need to force the push with --force
.
git push origin master --force