Use test mode via Bluetooth® connection

Check your Core's Bluetooth® device name in "System Settings". See here for details on how to check the device name.
Connect the battery box cable to the power connection port of the Core and switch on the power.
Press "Test mode" in the upper right corner of the screen.
Select your Core in the connection screen.
(iPad users only) Select "Pair" for the "Bluetooth Pairing Request" message.
(Windows 10 users only) You will need to go through the initial settings if you are connecting the Core for the first time. Please see here for instructions.
If you have set up a passcode for your Core, enter on the next screen.
Once the screen has been switched, an orange bar will appear on top of the screen.
To quit test mode, press "Quit test mode" in the upper right corner of the screen.