I really don’t think you can.
The whole purpose of this site is so that your clients can review you as a professional. When the public is looking for a fitness professional, they want to know what your client’s experience has been.
What I would do is the respond to the review online, address what your client is unhappy about so that you clients can see how you handle client dissatisfaction. If the review is unfounded, intelligent people who are looking for a professional will see the review and still decide to use your services.
Best to you.