Wow, IIRC that link used to be much easier to find but it seems like they don't want it to be found... :o
"Request Your Personal Information" help article: https://www.amazon.com/gp/help/customer/display.html?nodeId=...
amazon.com link: https://www.amazon.com/gp/privacycentral/dsar/preview.html
amazon.de link: https://www.amazon.de/gp/privacycentral/dsar/preview.html
(They don't even mention "GDPR" on that page but that should be GDPR compliant.)