To view your upcoming deliveries and their customization statuses, log in to your account home page. If your delivery is available to customize, items for substitution will show up on the page.
All of the produce items listed on the page are currently "In Your Box" and are scheduled to arrive in your delivery (before any customizations) for the date shown.
To make changes, you click or tap on the item you wish to swap out and a pop-up will show a list of items available for substitution. Choose the item you wish to receive and it will be updated in your menu. Notice the green "Sub" bar is now a blue "Un-Sub" bar.