Resetting Fitbit Charge 2
Connect your Charge 2 to the charging cable and plug it into your computer's USB port. Is the activity tracker vibrating? That lets you know it has started to charge.
Press and hold the button on the side of the tracker for 4 seconds.
You'll now see the Fitbit logo appear. Which is a good sign, because it means the tracker is restarting. Now disconnect the Charge 2 from the charger.