GarageBand for iOS: GarageBand may ask to access your Contacts

In order to automatically populate your name as the artist and composer of a song, GarageBand will ask permission to access information stored in your Contacts app. Additionally, GarageBand will use this permission to allow for ringtones or alerts you create to be assigned to a specific contact.

Select "Assign to contact" when sharing. This will allow you to choose a contact to the ringtone or text tone.