If you need to adjust the due date on an assignment or decide to push it back to give students additional opportunities to complete the assignment, you can do so in your Assignments subtab.
Click on the Classes tab, choose the class and click the View Class button.
Select the Assignments subtab.
Click on Options next to the assignment that you wish to adjust.
You will be brought to the first page of the assignment creation process. Click Next.
On the Assignment Settings page, you can change the due date.
Note: Students will get an email notification once you save the assignment with the new date.