Applies to: Moodle 3.0, 3.2.
Instructors can manually grade a quiz question or override an existing grade on quiz question that has been automatically graded. Instructors can also add feedback to a student’s quiz question answer.
If there is an error in a question after the quiz has been taken, the instructor can make changes for the whole class. See Edit Questions Used in a Graded Quiz.
If you are not sure of the question number, you can look at the entire student attempt:
Grade Essay Questions in a Quiz
Edit Questions Used in a Graded Quiz