If you would like to add a product through your account. Just log in click "Subscriptions" on the right side of your screen, click the green "Add Product" button, and scroll down to what you would like to add.
You will see "Charge Date" at the bottom. This is when your next refill will be. You can leave it as is or change it to whenever you would like it sent. Once you have made your selections just click "Add Product" and you're all set!