Go to Settings>General>Bluetooth.  If Bluetooth isn't on, turn it on. 

• If your iPhone/iPad is currently connected to another Bluetooth device:
  • Choose the paired device and tap Unpair

• If you have not been able to connect to your Bluetooth device, you will first need to remove it from the list.
  • Choose your Bluetooth device and tap Forget this Device
  • Follow the pairing instructions of your Bluetooth device