Situation: You may have a problem to use Fitbit device because it doesn’t pair Bluetooth no matter what you try such as disable/re-enable Bluetooth, turn off/on app, restart phone.
Resolution 1: Restart Fitbit device.
Go to the Settings.
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Go to Reboot
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Press Screen for 3 seconds to restart it.
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Resolution 2: Clear User Data or Factory reset – Note: you will lose all tracking data.
Repeat above steps until you see Clear User Data.
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After clearing the data, you may need to reset Fitbit.
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Please view this step by step video: