To skip an upcoming unlocked delivery click on the 'Deliveries' tab at the bottom of your screen. You will see a a calendar strip at the top of the screen, as per below, click on the date that you wish to skip.
Click on 'Edit Delivery' near the top of the screen. You will then be presented with the following options:
Click on the 'Skip Delivery' option.
To unskip a a delivery click on the 'Deliveries' tab at the bottom of your screen. Using the calendar strip at the top of the screen select the date you wish to unskip. You will know if a delivery is already skipped as the date will have a red cross above it.
Now you can simply click the 'Unskip' button.