Theme app extensions allow you to easily add your add-ons block to the right place of your store theme without having to interact with Liquid templates or code. The feature is only supported by the newer Online Store 2.0 themes.
Step 1: On the home page of your store's admin panel, click the "Custom theme" button
Step 2: In order to start using the Theme app extensions, open your theme customization menu
Step 3: Go to the product page and add a new block to the Product information section (or anywhere else you want it to be displayed)
Step 4: Select the Upsell app (don't forget to install the app first)
Step 5: Now you can drag-and-drop the add-ons to the best place on the product page
And on the cart page
