ThirstyAffiliates Pro customers are issued with a unique license key on purchase.
You can retrieve the license key for at any time via your My Account area.
Simply log in, then navigate to Licenses to see your key.
If you have installed your plugins on your website you will find the license key entry screen under ThirstyAffiliates->Settings->License tab.
Only once you have entered your licenses will you be able to retrieve plugin updates via your Dashboard (just like you would any other plugin).