Contact Websites/ Forums
Always keep this in mind that online reviews can make or break your brand reputation. The reason being is the customers want best and seamless service with lesser complications, that's why they consider the online review and comments of previous customers.
Besides the company's official site, there are other sites too where customers have the right to share their experience. If these reviews are positive then it's great and if negative then it's a problem. In this portals, there is no identity verification process and thus it becomes difficult to trace the person. Here, we contact the websites and forums directly. The webmasters and admins of these sites control the website contents. One can send a request for the negative content removal, it's up to them they accept the request or not.