On your home screen select the "cog gear wheel". This should bring up a list:
Account
Products
BeoLink
Music
Radio Support
About
Select this Music option and it will then display another list:
Deezer
DLNA
iTunes Library
Personalisation
Controls
Select the iTunes Library option and then enable by tapping the toggle option.
Then when you select Music at the bottom of the home page, scroll all the way down past your selected Deezer options and you will you can select music from your locally stored iTunes music; Songs, Playlists, Artists, Albums.
Worth asking if your Bang & Olufsen app is up to date, Should be version 2.5.19522
Regards
Opman