If you created an account Google my Business, connect on your page Google My Business.
At the bottom of the page, in "Establishments", click on"Managing the establishment".
Click on "Modify", next to the name of your restaurant.
The displayed page allows you to manage all the information about your restaurant (addresses, opening times, type of cooking) and to add an "URL to book". Click on the icon "pencil".
Click at the level of "URL to book" and copy the address of the link towards your module of booking or towards the page of booking on your web site. Click on "Apply" to record your information.
NB : You can use a dedicated url, which will open the Guestonline module and will pass on your bookings with a "Google" source. For that purpose, copy then stick the address from Guestonline Web, in the menu Settings > main Module
The bookings created from this link will display in your reservations note-book with Google logo: