When you do want to use an existing IoT Hub, you can also create an IoT Hub, a ux4iot instance and link them together right from the start.
The easiest way to do this is to push this button:
(GitHub repo for the deployed ARM template)
Please select one of the following Azure Regions as otherwise the deployment will fail:
West US 2
The resulting instance of ux4iot will already be configured with the necessary credentials to access the created IoT Hub.