It is never easy to get a poor review, and can be frustrating at times. However, review programs are here to allow other consumers to share their candid experiences and feedback, and help other potential consumers make an decision for patronage. You cannot control what others will say and if they felt they had a bad experience for one reason or another. However, you can control how you turn it around attempt to make the situation positive.
There are two things you can do. One, is posting a public response for future potential clients reading your reviews.
In your public response, you want to be short and to the point with a tone of empathy, diplomacy, a professionalism. You will want to apologize and address that the issue has been remedied. This will reassure potential clients that this will no longer happen if they come to visit you. You may want to clear up that the issue was out of your control, maybe their was a neighbor dog barking and you have since talked to the neighbor. This response is really for potential clients, and is not meant to be lengthy in communicating to the client who left the review. They will not get a notification of your response.
You can find the steps to leave a reply in the thread of the review on your account here: Responding to a Review.
Note: The client will not receive a notification of your response.
The second thing you can to do is send a personalized email to your client directly or give them a friendly call to explain, clarify, tell them how you have improved. You can even offer a credit or coupon for a future appointment, and thank them for their feedback and time. Making your true intentions clear in that you want them to have a excellent experience will go a long way.
You can find more information on creating an email to sent to a specific client here: Filtering Your Clients to Send Targeted Email Campaigns.