You need to use the correct words in order to control your connected "… with Netatmo" products using voice control with Google Assistant.
You can find a non-exhaustive list below:
1- For your connected lights
To turn on/turn off a light => say "Ok Google, turn on ".
To turn on/turn off a room => say "Ok Google, turn on ".
To turn on/turn off all lights => say "Ok Google, turn on all of the lights".
To brighten a light => say "Ok Google, brighten the light (*)".
To set a light brightness to a certain percentage => say "Ok Google, set to 50%(*)".
….(*) => Only when the dimmer feature is activated. See the FAQ "How does the dimmer option on my light switch work?".
2- For your connected power outlets
To turn on/turn off power outlets => say "Ok Google, turn on ".
….3- For your custom scenarios
To activate the scenario=> say "Ok Google, activate the [Scenario name]".
To enhance your experience, we advise you to go to the Google Support site. https://support.google.com/assistant