For an easy revert if it's just a mistake (perhaps you forked a repo, then ended up pushing to the original instead of to a new one) here's another possibility:
git reset --hard 71c27777543ccfcb0376dcdd8f6777df055ef479
Obviously swap in that number for the number of the commit you want to return to.
Everything since then will be deleted once you push again. To do that, the next step would be:
git push --force
