Update: The Fitbit iOS app has gone through a significant facelift since this was written. The “weird icon that looks like a card in the top right corner” is now the user profile icon in the top left corner.
The Charge 3 doesn’t actually have a calendar app. It can, however, display notifications from your iPhone’s calendar app.
In the Fitbit app on your phone, tap on the weird icon that looks like a card in the top right corner of the screen, then select your Charge 3 from the list of devices. Go to Notifications and make sure the Calendar Events item is turned on, go back to the Charge 3 page, then make sure All-Day Sync is turned on, then tap on Sync Now towards the bottom of the same screen.
As long as the iOS Calendar app is set up to generate notifications, that should enable them on the Charge 3. You shouldn’t have to do anything special in the iOS Calendar app to allow it to send notifications to the Charge 3, other than making sure that notifications are turned on for the app in the Notifications page of the Settings app. While you’re looking at that, also look to make sure that Notification Center is enabled for all of the event types for which you want to receive notifications.
If you’re interested in receiving notifications from a third-party calendar or to-do app, you’ll need to wait until it actually sends a notification to your phone. Once that happens, you can turn notifications for that app on or off in the Charge 3 -> Notifications -> App Notifications page.
Charge (r), Charge HR (r), Blaze (r), Charge 2 (r), Versa, Charge 3, Aria
