If you purchased your Mastering The Mix plugin directly from us, begin by searching your email for the subject line: Your Mastering the Mix product licence. This is the first step in finding your lost license.
If you don't find the email, please log in to your online account to view your licenses, download the installer and reset your licenses.
If you still can't find your license, then you might have purchased from one of our resellers. (Our main resellers are Plugin Boutique, ADSR, Audio Deluxe, Avid, Presonus, Plugin Fox, Don't Crack). If that's the case, you'll need to reach out to them directly to retrieve your license.