Just go to Author Central and set up an account. Once you’ve done that, you can claim your books and set up your author profile (and profiles for up to 3 pen names, if you want) and the system will begin tracking your reviews and sales for you automatically. It can take a day or two for books to be added to your profile, but it’s a relatively easy process. Once your books appear in your account, you can also do more advanced editing of their descriptions than is possible through KDP Print’s interface, although they have recently updated their interface in 2021 so the Author Central trick is no longer necessary. It does still give you access to other fields for your page, however.