The premium license you have purchased is linked to the account you used to make the purchase. You do not need any license keys to activate the premium plugin. You will just need to log in with the email address you used to make the payment for the premium plugin.
You can download the premium plugin by following these steps:
1. Login to https://auth.miniorange.com/ with the email address you used to purchase the plugin.
2. Navigate to the Manage License tab of the console.
3. You can find the premium plugin to download from here.