1. Go to the necessary course and click on This course > Grades
2. In the gradebook page, click on the assignment title i.e. Submit
3. Now in the Submit screen, click on View all submissions
4. Scroll through the cohort to find the correct student and click on the Edit button in the Edit column to view options. Then click on Allow another attempt
This will open-up a new submission for the student to re-submit their assignment.