It is complicated because Galaxy Watch Studio uses a library based on Internet Explorer that is seen as a security risk and not allowed to connect to the seller portal. So now there are hoops. Basically you need to download and install Tizen Studio and use their Certificate manager to create the certificates and then manually install them with an old Tizen installer called FitInstaller.
SEE THIS THREAD for details
I advise using Galaxy Watch Studio 2.0.0 and not the 2.0.1 version which has a nasty bug regarding the AOD unless you have a macOS computer
Ron
Samsung Developer Relations