Go to settings and ensure that bluetooth is turned on. You may see the message in the image.

The next step is allowing the app to access your location. Click Change to Always Allow to let the app see your location every time you use the app. You will not see this message the next time you open the app.

The Bluetooth will automatically detect the presence of the sensor. Then, a code will appear on the sensor. Enter the code into the app.

The sensor is now successfully connected to the app. You will see the carbon dioxide levels on the app every time you open the app.