Just drop a single measure on to the gauge chart and this will show you the measure as a gauge. Change the lower and the upper limits in the properties panel. Also you can colour code the range with multiple colours.
The extension works great but honestly I wouldn't use this. I don't think this improves upon the gauge chart already in Qlik Sense. It also won't export to PDF because it's an extension, whereas the stock gauge will export. Gauges are also kind of shunned now in the data visualization design world. They're too busy and take up too much space on the page. Just some feedback for you, hope it helps you in your future extension building.