Just turn off the Bluetooth, reboot your device, and once you turn it on again, check if the Bluetooth is working.
For many issues, toggling Airplane mode is the fix. Turn it on, leave it that way for 15 seconds, and turn it off.
Go to Settings, tap on General, Reset, and click on Reset Network Settings.
Back up your files. Click on Settings>General>Reset>Erase All Content and Settings. After this, your device will reboot, and then you should follow the given steps to finish the setup.