OK, found after a very long search.
I've found via using help.
The link isn't listet in my account for changing that.
If someone is searching like me:
"paypal.com/de/cgi-bin/webscr?cmd=_profile-sales-tax".
I just got an answer from paypal.
They know about that problem. Not all customers have that links but they are working on it.
The paypal support wrote:
die fehlenden Links sind uns bekannt, wir hoffen diese bald innerhalb des Kontos anbieten zu koennen.
