You probably already experienced the situation where it was impossible to deliver a parcel but the driver did scan it anyway or the opposite, where a driver forgot to scan a parcel, that was actually delivered. In these cases you will have to adapt the items' status manually to 'delivered' or 'impossible to deliver'.
When you open a task, underneath the list of items you will see the button 'modify'.
By clicking on it, the following screen will appear:
There is a line with a checkbox for every item in the task. The checkbox allows you to change the status per item.
On the right side of the window, you can indicate the date when an item was delivered (or not) and if the delivery was impossible, you will also be able to choose the reason for non-delivery.