Disconnect Nintendo Network ID associated with Wii U?

I recently bought a new wii u, a few years ago i sold my old wii u. At that time I did not disconnect my linked nintendo network id there. But I remember that I bought and downloaded many games that I do not want to buy again, of course.
If I now want to connect my new wii u with the network id, an error message comes that this is not possible. How can I disconnect via pc the network id connection to the old wii u konsole, so that I can connect these with the new wii u?

If you can't find any help here, I would write an email to Nintendo, they have always been able to help me with any problems.