You should create a branch for each of your stories. You should be able to push your branches to the origin server, and Code Review should occur when you create a pull request to merge a branch into the master branch.
If your current code is not yet in a separate branch, then create a new branch for it, switch to the branch you were working on, and perform a hard reset to the commit that you want to base the new story on. Then create a new branch for the new story.
After you're done with your new branch, you can switch back to the old branch: