Occasionally, something will go wrong with a student’s assignment submission. In this case, the easiest thing to do is to clear the assignment attempt and let the student resubmit.
To allow a student to resubmit his or her assignment,click on the test in question in your Course Content feed and click Submissions on the top right.
You'll be brought to the list of students, complete with their attempts. Click on a given student's name to enter their attempt.
You'll be brought into the attempt itself. In the top right a Submissions receipt number will be visible, as well as a grade if all questions in an attempt have been graded and a three-dots icon for additional options. Click the three-dots icon and select "Delete" from the resulting dropdown menu. You will be asked if you are sure you want to delete the submission; click "Delete" to complete the deletion.
Once you do, the entire attempt and any feedback that you’ve given will be cleared, and the student will be able to resubmit.