Click on the "Completed" tab.
Select the assignment that you want to review and click on the "Report" button.
You'll have a detailed page with all the items included in the assignment and their grades for each student.
Hover over the points of the student that you want to reset the attempts for.
Click on the check box to enable the option to reset the attempts
Click "Yes" on the prompt message
You will see that all attempts have been reset.