Settings for the time format of your Fitbit is found at the Fitbit Account Settings website.
1. Log into your Fitbit Account Settings.
2. Scroll to the bottom of the page until you reach the “Advanced Settings” section.
3. Click “Clock Display Time”, and select “24-hour” or “12-hour”.
4. Click “Submit” near the bottom of the page.
4. Open the Fitbit app on your phone and swipe down to sync the app
Change to 12hr/24hr Format (YouTube Video)