"To contact the reviewer" means to reach out or connect with the person who has reviewed or critiqued something, such as a product, service, or work, in order to provide feedback, ask questions, or address any concerns. Full definition
It's also a good idea to contact reviewers who are active in your particular genre, as they're more likely to take you up on your offer. (authorsecret.com)
You may not be able to contact the reviewer directly but there are a few things you can do to minimize, improve or reverse the review. (bookrevieweryellowpages.com)
The logistics of contacting reviewers with advanced review copies and making sure they can download the ebooks to their readers of choice. (marketingsff.com)