A Task 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 task as well.
Any Delay in Task Constraint will be recorded with the reason for delay and the responsible person for the same.
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 the Pencil (Edit) button for the last step(condition) of the constraint
Select the date and click Tick button
The constraint due date will update accordingly with the changes to the last step (condition)
The steps to update an Activity Constraint Due Date is similar to update a Task Constraint Due date, 3.20 Update Activity Constraint Due Date article to know more.