The Native instruments Komplete Select 15 Bundle is only included with the Impact LXmk3 controllers. This page on the Native Instruments website seems to indicate that the Impact LX+ controllers are NKS compatible and come with a copy of Komplete Select 15. That is not correct.
If you have purchased an Impact LXmk3 series controller, you should have a card which is included with the printed user guide. That card has a code for Komplete Select 15 printed on one side and a Bitwig 8-track code printed on the other. You can claim the bundle by using the code on this page: https://www.native-instruments.com/en/products/hardware-partnerships/nektar-partnership/
If you have purchased an Impact LX+, you are not eligible for the Komplete Select bundle but you may be eligible for the Cherry Audio bundle. You can find more information about that, on this page: https://nektartech.com/nektar-software-bundle/