To find your Facebook Review URL, go to your Facebook Business page, click Reviews and then copy the URL and paste it into the form. Here's a video showing you how:
https://youtu.be/Sl3NtfNBxNY
Note: If you do not see the Review tab on your Business Page, this means that you have not enabled reviews on FaceBook and we can not add this to your Review Management form until you enable Reviews.