If your organization has a Visual Studio subscription (formerly MSDN), you can download the of Windows Server 2019 Standard ISO – not just an evaluation.
To ensure the security and integrity of your server, it is vital to download the ISO only from authorized Microsoft sources. Microsoft Evaluation Center download microsoft windows server 2019 standard iso
If you have an Azure subscription:
Will you be deploying this server on a or as a virtual machine ? If your organization has a Visual Studio subscription
As an administrator, run DISM /online /Set-Edition:ServerStandard /ProductKey:YOUR-PRODUCT-KEY /AcceptEula , then restart your server. then restart your server.