As the teacher you can edit a student's rubric response. Go to the Results page and find the student who's rubric you want to edit. (If you want to fix the scores that John got make sure you're on the Submission tab.)
Find the question you want to edit and click Edit Response. A popup will appear that will allow you to change the answer.
After you have changed the answer it will show in the comment section that the answer has been overridden.