Sorry, first didn't see that you most probably don't speak/read German: THe official website (https://www.coop.ch/en/locations/coop-supermarkt-muenchenbuchsee/1084_POS) lists the Coop here.
The address node (https://www.openstreetmap.org/node/6389375754) is given close to the parking entrance, and there's an outline of an underground building visible on the cadastral layer we have available in the Canton of Bern.
