If you've elected to skip a box but change your mind you can unskip the delivery as long as you do so before the end of the customization window for the order.
To unskip an upcoming box:
Step 1: Log into your account.
Step 2: Click 'Delivery Schedule' from the menu on the left-hand side.
If you're on a mobile device, click the white dropdown arrow and click 'Delivery Schedule'.
On this page, you'll see a schedule of your upcoming deliveries.
Step 3: Click "unskip" on the order you'd like to unskip.