This article only applies to the old designer. Not sure which designer you have? Check here.
While you're working on your design, you may notice the gift, terms, and variants pages aren't in the pages dropdown of the visual designer. This is because they're all part of the subscribe.html page.
In order to edit these pages, you can click on the actual button or link on the page within the designer. You can navigate around to any page within your design in this same way if a page isn't visible in the pages dropdown.