First you have to install Grand Restaurant version 1.9 or higher. Then open WordPress Dashboard > Menus and select menu item you want to add order option.

Screen Shot 2559-05-13 at 11.11.06 AM

You will find “Order URL” in Menu Options on the right sidebar. Enter URL of order page. It could be external site or you can also link it to Woocommerce shop page Then click “Update” button