Rewinding to a specific commit hash in the repository.
Check the log for the commit hash.
Find a commit to roll back.
commit b331419ad4cc4397a3138d3fc1166be014debc4f Author: Firstname Lastname <firstname.lastname@example.org> Date: Sat May 16 21:31:20 2015 -0400 Setting a short name for the application; useful for deployments.
Reset the repo to that commit.
git reset --hard b331419ad4cc4397a3138d3fc1166be014debc4f
Now push that commit back to GitHub.
git push -f