Please go to “Shop Manager”. From the left hand panel select “Promotions” → “Embed Shop to Facebook”. Follow the instructions provided on the page.
To embed your shop, you have to be an admin for your Facebook Page. A pop-up will appear, requesting your Facebook login. If you don't see the pop-up, please check that your browser is not using a pop-up blocker. Once logged in to your Facebook account, you will see your Pages. Choose the Page you want to integrate your shop with.