Activate Bluetooth® in your playback device. Push the multi fuction button (= the middle button) of the earphone during approx. 6 seconds, until it shines blue permanently and doesn't blink anymore. The headphone model then will appear in the list of available Bluetooth® devices in the menu of the playback device with the respective product name ("beyerdynamic Byron wireless" or "beyerdynamic Byron BTA"). Choose the earphone and it will be connected for music playback (and for calls on a smartphone).
This connection called "pairing" needs to be done only once. Each time afterwards Byron wireless and Baron BTA will automatically connect with the playback device.