In the event that you have several "… with Netatmo" connected installations paired to the same Legrand - Netatmo - Bticino user account, all of your installations connected switches and power outlets can be accessed from Google Assistant without differentiating between your installations.
If you want to control a "… with Netatmo" connected installation individually with Google Assistant, you must pair the Google Assistant with a Legrand - Netatmo - Bticino user account that is only linked to this installation.
From the Home + Control App, you must:
Either create a new Legrand - Netatmo - Bticino user account that will only be paired to this installation. Go to settings in the Home + Control App and invite yourself to share this connected installation on another Legrand - Netatmo - Bticino account with an address that is not currently used. See the FAQ "How can I share my access to the installation with other users?".
Or remove access to the other installations paired to this account and only keep the installation that you want to control with Google Assistant. Select the home in the App that you want to remove and in settings, select "Manage my guests", then remove the account by tapping on the corresponding cross next to the linked email address.