To add, remove, or edit all of your activity due dates at a glance, click the drop-down menu next to your course name at the top left corner of the dashboard. Then, click the ellipses ⋮ next to the applicable course and select "Edit Activity Due Dates."
You can adjust the due dates all at once using the "-1 Day" or "+1 Day" options. Or, you can edit the due dates individually by selecting the calendar icon next to each activity name and choosing your dates. When finished, click "Close."
Alternatively, you can adjust the dates for a single activity by clicking the ellipses ⋮ next to the activity name on the dashboard and by selecting "Edit Activity". Then click "Edit" at the top right of the activity settings and enter your dates. Click "Done" and "Close" when finished.