How to Control audio from the Now Playing card
1 Take control of music
When an app is playing audio in the background, Control Centre’s second card shows details (tap them to go to the app), playback controls, plus headphones, Bluetooth speakers and AirPlay speakers you can send the audio to (one at a time).
2 Pick a target on iPhone
On iPhone, the current destination for audio is shown in the bottom row of the card. Tap it to expand it and see the list of available speakers. Tap one to send audio to it, then tap outside of Control Centre or swipe down on it to close it.
3 Split video and audio
You should also use the second card if you want to watch video on your device yet send its audio to a better speaker; ignore the first card’s AirPlay control in this instance, as it always sends video and audio to your specified destination.