Coaches:
A coach can send a push notifications to their clients by writing '@community' inside any bulk message or community chat message.
Clients:
A client can send a push notifications to their clients by writing '@community' inside any community chat message.
Note: push notification by using '@community' must be done when logged into your account via web browser, NOT through either the coach or client apps.
To chat in a community
Head to the inbox area and the communities tab and you'll see all the ones you're part of: