The studio writes each edition's ebook from its manuscript: chapters and parts in the right order, a table of contents readers can tap, the language set on every page, and the title, author, ISBN and publisher in its metadata.
What you need: the edition's manuscript, and its ebook ISBN if you have one.
What you get: an EPUB you can upload to KDP and the other stores yourself. Every build is checked with EPUBCheck before you download it. Its metadata tells stores and readers what it offers people who read with a screen reader or braille: a table of contents, structural navigation and, when every picture has a description, text alternatives. The accessibility guide says what the EU's law asks of an ebook and what each store asks.