How does a new KDP writer supposed to market a book?

Because you cannot persuade readers to buy any book in which sentences do not make sense. This shouldn't be “does.” If you don't see the problem, that is a big problem.

D) that are presented with bad covers, bad descriptions, or ludicrously bad interior formatting.

B) Build a newsletter mailing list of people who will buy your book because they trust you to write books they want to read. This is slow, but ideal.

Harvard gastroenterologist shares 4 bloat-busting tricks that actually work - Times of India

E) Take a solid year to learn how to use Amazon or Facebook ads and be prepared to lose quite a bit of money as you figure it out.

D) Pay promotion services like Written Word Media to promote your book. Legitimate services will not accept your book for promotion if the presentation is crappy or the book is badly written.

C) Persuade book reviewers on BookTok or Substack or someplace to recommend your book. If your book is unreadably terrible, this is probably impossible.

Anxiety and anger may explain how parenting styles shape life satisfaction - PsyPost

A) Build a following on social media, a following of people who will buy your books. Good luck with that. There is very little evidence that social media can translate to sales.