The "delete" function is available in your Google My Business listing.
Type the name of your restaurant into Google and select Reservations.
A window opens and you can choose which supplier to delete.
By clicking on "delete" you will be redirected to your supplier profile settings.
There you can deactivate / disconnect from the Google partner.
As a reminder, there is a delay of a few days before the button is no longer visible on the GMB page.
The process is not the same for all suppliers.