You can send push notifications from the MCD website. Go to Members Centre, select Tools, Push Notifications.
Select Send a New Push Notification and the following screen will appear.
You can selected the audience who will receive the notification. This can be everyone who has installed tiles from an organisation. A specific tile group, or a single user. Enter a title and the body text for your notification. You can also add advanced options. These are to display a popup message in the app, and also do a Directory or Diary search within the app.
Tapping Send will push out the notification to the recipients.