Steps
- Open the calendar view and select Availability.
- Select Import and export.
- Copy the HomeToGo export link.
- Create the HomeToGo source and paste the link as its import URL.
- Copy the kalenderabgleich.de export URL and import it into HomeToGo.
- Save and remove every other connection.
Final step: Remove all old direct calendar connections to other portals from the provider. Only the kalenderabgleich.de calendar should remain connected.