If you have several "... with Netatmo" connected installations paired to the same Legrand - Netatmo - Bticino user account, all the connected products of your systems will be accessible via Amazon Alexa without distinguishing between your systems.
If you want to individually control a "... with Netatmo" connected installation via Amazon Alexa, you need to pair a Legrand - Netatmo - Bticino user account that is linked only to this system.
Via the Home + Control App, you need to:
Either create a new Legrand - Netatmo - Bticino user account that will be paired only to this system.
Go into the settings of the Home + Control App, create a new account (new e-mail address) and share this connected system.
Or remove access to other systems paired to this account and keep only the system that you want to control with Amazon Alexa.
In the App, select the home that you want to remove: in settings, select "Guest management", then delete the account by selecting the paired e-mail address.