Enabling/disabling client reviews is controlled on a staff level. This mean's each staff member has an option whether they would like to enable or disable.
Navigate to the Notifications settings page by logging in as the business owner and navigating to the name on the bottom of the side menu to navigate to your own Profile page. Example in the screenshot below is "Mark Liam".
Click on "Notifications Settings" on this page and scroll down.
Enable or Disable that switch at the bottom of the page called "Ask for review email" and your finished.