Hello there,
You have three options to migrate your RDS CALs:
Automatic connection method: This recommended method communicates via internet directly to the Microsoft Clearinghouse outbound over TCP port 443.
Using a web browser: This method allows migration when the server running the Remote Desktop Licensing Manager tool does not have internet connectivity, but the administrator has internet connectivity on a separate device. The URL for the Web migration method is displayed in the Manage RDS CALs Wizard.
Using a telephone: This method allows the administrator to complete the migration process over the phone with a Microsoft representative. The appropriate telephone number is determined by the country/region that you chose in the Activate Server Wizard and is displayed in the Manage RDS CALs Wizard.
Migrate your Remote Desktop Services Client Access Licenses (RDS CALs) https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/migrate-rds-cals
Hope this resolves your Query !!
--If the reply is helpful, please Upvote and Accept it as an answer–