You can try :
Step 1. Activate the function of Bluetooth on your mobile device and the car stereo respectively.
Step 2. Enter to the Bluetooth setting on your mobile device and search the available device to select the car stereo as the target device.
Step 3. Launch Spotify app on your device and start to play favorite Spotify playlists, and the playing audio tracks will be streamed to the car’s audio system.
or you can try another old school method- to burn CD from Spotify by using
Spotify Music Converter then play on your car.