Is this an issue where you played D2 on Battle.net, then when D2 migrated to Steam you neglected to migrate your Battle.net account to Steam for the 14 months the PC Move function was available to users? If so, nothing can be done now. The PC Move function was the one and only way to migrate your D2 game progress and licenses to Steam. It was available from mid September 2019 through December 1, 2020 at which point the service was discontinued.