Please confirm you have Bluetooth turned on, on the smartphone.
Confirm that the device is powered on, turned on completely, and is responsive to button presses.
The app scans for devices periodically, so user can try waiting for a minute or so for initial connection. Typically device is seen in 5-10 seconds but there may be differences based on the OS/ version / hardware.
Try tapping on the tile showing the Device under the "Vehicle" to refresh its status.