- Find the original commit your branch was on before you pulled.
ORIG_HEAD points to the original head of a branch before it was changed in a drastic way. "Drastic" means something more than a simple commit, like git reset or git pull. Verify ORIG_HEAD points at your pre-pull commit with git log ORIG_HEAD.
If it isn't, you can use git log --graph --decorate to find the commit before the pull. Or you can use git reflog to look at where HEAD was every time it changed.
- Reset the branch.
Assuming it's ORIG_HEAD: git reset --hard ORIG_HEAD
This will move the branch back to the specified commit as if the pull never happened.