Sometimes there are technical difficulties and a student will submit a quiz that is either empty or only partially filled out. In cases where you would like to give that student a fresh start you can delete their own attempt so that they can make a new one, unaffected by the erroneous grade.
If you want to keep record of that old quiz grade instead consider giving them an additional attempt at the quiz instead.
Enter the Quiz activity in question.
Click into the Attempts link.
Locate the name of the student.
You can filter results by name to make them easier to find, especially if there are multiple attempts permitted per student.
Check the box on the far left for any attempt(s) you want to remove from this quiz.
Scroll to the bottom of the page and click the Delete selected attempts button.
Click the Yes button to confirm your changes.
The student can now re-attempt the quiz assuming it’s still open and available to them. Depending on the situation you may need to give them a time extension.