Comentário oficial
@gagan > You are allowed 2 installations, but they must both be to the same email address, so your friend's activation would be on your account (with your license).
In order to deactivate your installation, you would need to be able to open rekordbox. If you are having problems with that, you can file an inquiry ticket here with our support team and they can assist you further in troubleshooting that issue or simply deactivating the installation.