How do I sync tags to a forked github repo?

You would need, in command-line, to fetch tags

git fetch --tags upstream

Assuming upstream is the remote name referencing the original repository URL.
(If not yet defined: git remote add upstream https://github.com/original/repository).

Then push tags to your fork

git push --tags

If you want to push only the tags from the branch you are pushing:

git config --global push.followTags true

That way, a simple git push is enough.