Once you've completed the Rent-to-Own program for your KORG plug-in, you can find your serial key here: https://splice.com/plugins/your-plugins
You will need to register the plugin products at KORG ID (https://id.korg.com) to unlock them. To do so:
Create an account at KORG ID
Download the utility software called KORG Software Pass at https://id.korg.com/ksp
Launch KORG Software Pass and login
Click "register product" button to start registration
Input the product code to complete registration
If you need to activate your KORG software a new device, simply log into KORG Software Pass and enter the serial key for each product in your DAW on the new device.