You did not say what version of CB 8 you have. The Artist and Pro versions have their license stored on a USB eLicense dongle. Other (lesser versions) like Elements start off with the license stored on the computer (called a Soft-eLicense). So just read the following help center article for the procedure to follow which is dependent on on your situation and which license you have.
My guess… probably “Reactivation” for a version that has it’s license stored on a Soft-eLicense. If the license is stored on a USB dongle (which would be plugged into a USB port on your computer) you don’t need to reactivate it. Just make sure the dongle is plugged in and install the eLicense Control Center and Cubase software.
Regards 