Yelp and other review sites such as Google, Facebook, Yellow Pages, Dex, Trip Advisor, RipOff Report, BBB, etc., all have the right (in the USA) to legally store and display user-created content without being liable for its content. Long story short, they don’t have to remove anything if they don’t want to, with a few exceptions.
I’ve gotten hundreds of reviews removed over the years and had people let me know this helped them remove reviews hundreds of times. If you stick to the process outlined here, it will give you a fighting chance!