You'll be able to activate your computer/device to your rekordbox subscription plan directly from your rekordbox 6 software following the steps below:

• Open your rekordbox ver. 6 software;
• Log in to your rekordbox account (making sure your credentials match your AlphaTheta online account login details as you used to download rekordbox ver. 6)
  When you subscribe to a Core / Creative plan, your subscription is associated with your AlphaTheta account, so make sure your credentials match those used when purchasing your rekordbox subscription.
• On the top-right corner, click MY PAGE and select the PLAN tab;
• Toggle the ON/OFF button to activate your Core/Creative subscription plan to your computer/device;

And that's it! You can then proceed on connecting your DJ unit and you are ready to play and enjoy! 🎧