I bought used maschine mk2 few years ago and tried to activate the hardware in order to get free maschine software but it says that it's already registered, the problem is that the previous owner is not available to get in contact with.
Hello, please read this article and then contact NI Support by using the links in the article.
https://support.native-instruments.com/hc/en-us/articles/360001301669-My-Serial-Is-Already-Registered-to-Another-User-Account