Simply choose the Kahoot, press play, under General Lobby Music is at the top.
Embedded below is Kahoot's Tweet as well as a 1 minute and 19 second YouTube tutorial so you can see and hear the music.
🤩 Now you can easily change up the lobby music when you play a kahoot 🎶 🎧— Kahoot! (@GetKahoot) February 1, 2020
👏 The best part- it's FREE for everyone🎸 pic.twitter.com/F7Sy5p4ByU