To add, remove, or edit all of your assignment due dates at a glance, click the ellipses ⋮ to the right of your course name, and select "Edit Assignment Due Dates."
To adjust the due dates all at once, use the "-1 Day" or "+1 Day" buttons. To edit the due dates individually, select the calendar icon next to each assignment and select the new date. When you are finished, click "Close." (Changes are automatically saved.)
Alternatively, to adjust the dates for a single assignment without opening this editor, click the ellipses ⋮ next to the assignment name and select "Edit Assignment".