An Activity Constraint can be delayed or advanced by changing its due-date. If an Approval constraint gets delayed, its due-date can be simply set to a future date to delay the constraint. This can result in delaying the Activity as well.
Any Delay in Activity Constraint will be recorded with the reason for delay and the responsible person for the same. The Delay History tab shown on click of a constraint will display the details of the delay.
The following steps guide you to Edit Due Date:
Double-click on the Constraint (indicated by a circle and in-lined with it's activity)
Click Pencil (Edit) on the last condition of the constraint
Select the new due date of the last condition
Click Tick
Editing of Constraint due date can be done in both the Masterplan and the Lookahead.
The steps to update a Task Constraint Due Date is similar to updating Activity Constraint Due date, read 4.14 Update task constraint due date to know more.