Contacts and calendar app: 1) stack processing 2) new birthday calendar

I have installed Nextcloud 13.0.2. Now I have two questions about the apps for contacts and calendars:

1. Can I edit or delete several (or all) contacts at once?

I would like to assign multiple contacts to the same group in one go. In other cases I would like to delete several contacts at once?

So far I have only discovered the possibility of editing or deleting individual contacts. This method is very tedious if you want to edit several contacts.

2. Can I reinitialize the calendar “Birthdays”?

At the beginning I had a calendar with the birthdays. The synchronization also worked. Then I renamed the dav-account on my smartphone (Android). I deleted all contacts on the smartphone (but forgot to delete the birthday-calendar) and importetd the saved contacts new. The result was that I got a birthdays calender with dobble-birthdays. That was the reason that I deleted the birthday calendar.

Now I would like to re-initiate this calendar list. In the “Settings” (see “Administration” in the “Additional settings” section) there is the field “Automatically create a calendar for birthdays”. This field i thought to be usefull to reinitialize a new birthday calendar. But you can not remove the check mark there - better said: You can remove the check mark, but the system obviously doesn’t save it as a new setting.

Is there any way to solve my problem?

I am grateful for helpful advice.
Best regards,