You can change a User's due date for an Activity via the Users tab of an Activity.
Note: This guide explains how to change a User's due date for an Activity via the Activity itself. You are also able to do this via the User's profile.
Locate the Activity you need to change the due date for and go into its administration area (see find content in Find Learning or Content Manager if you're unsure how to do this).
You will see a list of registered Users. Search for the relevant User(s).
You can also filter the list of registered Users by completion status using the dropdown menu. You may only want to change the due date for Users who have Not Attempted the Activity or are part-way through it (Incomplete).
Tick the box next to the User(s) name(s).
Note: If your intention is to manage ALL registered Users, make sure you click Select all items.
Choose Set Due Date from the Actions dropdown menu.
A popup will open in which you can set the desired due date. If a due date was already set, you can also choose No due date. You can also add a note explaining the change. Adding a reason helps if you have multiple Administrators or if you need to see why the due date was changed sometime after it happened.
Click Save Changes to apply the new due date.