I just purchased a Komplete Audio 1 second hand through Amazon and I'm unable to register the product in Native Access because the serial number has already been registered
You have to contact support through the Account and registration support page. That would be the only way to resolve the licensing issue.
https://support.native-instruments.com/hc/en-us/sections/360000092577
support link inop
Please read to my Support page functionality changes post here !