For me (amazon.de, EN language setting): Open app -> "More" burger menu botton right (three horizontal lines stacked on top of each other) -> Scroll down to "Customer service" -> Scroll down to search feature -> "Personal Information" -> #1. I think this is really just a webview to the same part of the website with a different design.
Takes a bit more tapping and scrolling than clicking on desktop, but that is more he fault of the smaller screen and how apps work I would guess.
Ah, it was only like 5 options deep and then it gave me a chat "assistant" which I used to search the term "my data" which gave me the link and the drop down box mentioned in the article to scroll to the bottom of to request my data. Which sent an email to my husband's email address that I need to open to confirm the request. Super easy. Not hidden at all.
Takes a bit more tapping and scrolling than clicking on desktop, but that is more he fault of the smaller screen and how apps work I would guess.