If you didn't download the plugin immediately on the thank you page after purchase, you should have also received an email with your license key and download link.
However, if you didn't receive this email, there is still a way for you to recover your own download and license key. Simply click the "login" link on LinkWhisper.com or go here: https://linkwhisper.com/forms/control-panel/ . Use your purchase email address as your username and you may need to click the "Forgot Password?" link and the email address used at checkout will be emailed with a password reset option.
Once logged in, you will find a download link, your license key, and the ability to manage or upgrade your account.