1. Log in to your Merchant Center and navigate to the "Settings" tab
2. Scroll down to "Presence/Review Sites"
3. Click the "Edit" button in the top right-hand corner of the Facebook box
4. Paste the URL of your Facebook page into the field at the bottom
5. Click "Save Changes" in the top right-hand corner of the box
A direct link to leave a review on the page will generate upon saving.