Thanks for the solution!
Update account data with more calendars
I use on the server-side OwnCloud. I can create different calendars for one account. When creating the DAVDroid-account I can select which calendar(s) I want to use.
But if I already created the DAVDroid-account and add an another calendar in OwnCloud, I am not able to add this calendar on my Android.
Indeed, please see http://davdroid.bitfire.at/faq “How can I change the URL/user name/password of my DAV resource or add a new calendar?”
I know that would be useful but it’s quite complicated and not scheduled at the moment (of course, pull requests are welcome).