You can reset/deactivate your Phantom license in 2 different ways.
1. Navigate to the settings section of the bot (gear icon in upper right hand corner), and then click red Deactivate button.
2. Find the Phantom discord bot (Phantom#8170).
DM the bot the command !reset XXXXX-XXXXX-XXXXX-XXXXX-XXXXX (the Xs being your key). If the bot returns License key reset., your license key was successfully deactivated. (In this example, I send !reset THISI-SPROP-ERTYO-CACTU-SJACK to the discord bot and it returns License key reset., thus my license key has been deactivated. No, this is not a free key.)