Hello,
To sell a license you will need to remove it from your account here on the forums and then send us an email at
support@mixvibes.com from the email registered to the forum account (or let us know what that email is if using a new/different one now).
In that email also let us know the license key and if possible have the buyer reach out to us after purchasing so we can make sure everything registered correctly.
Regards,
Adam @Mixvibes