On the navbar, click Quizzes.
On the Manage Quizzes page, from the context menu of the quiz with attempts you want to reset, click Grade.
Select the check box for each attempt you want to reset and then click the Reset icon at the top of the list of quiz attempts. Note: By default, the Grade Quiz page only displays completed quiz attempts. To view quiz attempts in progress, on the Users tab or the Attempts tab, from the Restrict to filter, select either All attempts or Users with attempts in progress.

Watch how to reset quiz attempts for learners

Reset quiz attempts for learners