2.5 | Adding Templates to Products
You can only add a template to a product (or products) once the theme is live or published, so if you are using this as a refresher and starting afresh with an OS2.0 theme or a new theme your new templates will not be available to add to the products.
Once your theme is live or published, go to the page and on the right at the bottom in the Online Store section choose the template from the Theme template dropdown.
You can now also click on Customize template and click straight through to the page template to make any edits or updates.