You connect your scanner to the app in the Account tab. Tap 'Device Settings' and then "Search for devices'. The app will list the active scanners that are in reach of your phone or that have been connected to your phone in the past. Check the device name on your scanner as shown in the image below. Tab the correct scanner to connect.
Sometimes the app does not locate the scanner immediately. In this case you first need to access the scanner via the general Bluetooth settings on your phone. You can activate your Bluetooth in the device settings, or in the drop-down menu. Try re-synchronizing the Bluetooth list and see if the scanner device appears. Try also connecting the scanner from the Bluetooth list in your phone's settings.
For more detailed information please read the article connection and Bluetooth.