This isn't a feature on the system where it will prevent Users from confirming future delivery dates on orders, as delivery dates do change. There is a permission Restrict date adjustments under Order Management within Roles. This prevents user moving the delivery date to a date before the order was created. If you have access to amend roles and to enable the permission, please follow the below steps:
Go to the Admin Cogs
icon then click Organisation Administration tab.Click Roles tab.
Edit relevant Role.
Click Order Management from left hand side menu.
Scroll to Restrict Delivery Date Adjustments.
Tick box.
Click on Update.