The Target Due Date in a Creative Brief is the date the item is scheduled to be completed. This is the date associated with the Content Item in the Editorial Calendar as well as the Complete Stage date in Workflow.
Clicking on the Target Due Date Field will open a Calendar where you can select a new Target Due Date, as needed. Once you select a new Target Due Date you will need to confirm the change as it could impact other Stage Due Dates within the Workflow assigned to the Content Item.
Another way to move the Target Due Date is by dragging and dropping a Content Item within the Calendar. The same rules regarding changing this date apply.