The fitness tracker itself does not do timing by itself, it just reads and follows your smartphone’s time and format, the time/date on your tracker will update automatically when you pair your fitness tracker with the H Band app via Bluetooth on your smartphone. You can try to reconnect ( Mine > Y39 > Disconnect ) or logout from the H Band app ( Mine > Logout ) and login again to pair it.
To learn how to pair your tracker with the app, please watch the short video at our help center: