He added the two parts mentioned in his first post to his installation and connected the Opener to it. With the help of the Nuki support he got everything up and running.
Problems is that if you live in a multi party building you can not add this two parts (Schaltaktor & Tasterschnittstelle) on your own as they require pairing and this can only be done by someone who has access to the main Gira hub in the building.