Under Course Management in the lower left of your course site,
- click on the Grade Center link, then
- click on Full Grade Center. Find the column for the quiz in the Grade Center spreadsheet and match it to the row with the student who needs to retake the quiz. Where the column and row meet, click the double-down arrow button. From the drop-down menu, click View Grade Details. Click on the Clear Attempt button. When prompted, click OK to clear the attempt.