You need to claim your business page to be able to respond to reviews, and you will be able to do so through a comment.
Comments made will be visible to anyone that views your business page, including the general public. Follow the instructions below:
1. Click on the Reviews page of your business account
2. Locate the review you’d like to respond to and click on the “Comment” option
3. Write out your response
4. Click on the right arrow button to post your comment
If you would like to remove your comment, please click on the ‘Delete’ button. You also have the option to edit your comment by clicking the “Edit” button.