Unfortunately, it is not currently possible to change the music of an application. You can only play with or without the music we chose for the app.
However, you can mute the sound of the Lü app from the setting and play the music from other media such as YouTube, Spotify, Apple Music, Amazon Music, Google Play Music, etc. at the same time. For example, you could create your own playlist and play it while playing Lü.
1. Go to the Lü application’s settings and uncheck the boxes under the Audio section to disable the music and the sound effects
2. Then, open a web browser using the internet buton on the keyboard.
3. Go to the website you want to use and start your playlist. (for example : Amazon music, Spotify, Deezer, Google Play, Youtube, etc.)
4. When your music is playing, press simultanuously "Alt" and "Tab" to switch from a window to another.
With Spotify, you can connect your cell phone and/or tablet to control Spotify on your device. This way, you could play the music through the Lu sound system and control the volume from your personnal device.For more details, click ob the following link: https://fr.wikihow.com/synchroniser-son-compte-Spotify-sur-d%27autres-appareil