If you already created a PastBook Yearbook or a Facebook Highlights book, click on the "Checkout" button and you will see an option to add the Calendar to your order. Click on "Add to Order" button and proceed with the checkout*.
After selecting to add a Calendar to your book, you can also select the size of it.
Once the size has been selected, you can also choose the amount of copies for both the PastBook and your Calendar.
*If you don't have this option on the Checkout, please let us know and we'll check it for you. It might depend on your device or country.