i think you can still deactivate from customer portal... or reach out to support via ticket and they can give all possible options..
You can request the license to be deactivated via a ticket in the Customer Portal.
1. Go to Customer Portal Login | SolarWinds and log in.
2. Under the Technical Support menu, click Open a Support Case
3. Select the Licensing option and fill in the request details.
If you have multiple licenses, specify which license key should be deactivated.