Easy Digital Downloads (the plugin we use) has an area to manage licenses inside your account: https://generatepress.com/account
Under “Purchase History”, click “View Licenses”, and then “Manage Sites”.
That being said, I’m not fully convinced it actually works, and EDD doesn’t offer any documentation for it at all.
If you don’t have access to their Dashboard anymore, the only way I know will work 100% is to regenerate your license key. However, this is a pain if you’re using it on a ton of sites.