1. Launch CMD Elevated
Click on Start and then type in CMD and right click on it and select "Run as Administrator".
2. Open Exchange 2019 ISO
In your downloads folder, double click on the Exchange 2019 ISO and take note of the drive letter.
3. Start running commands
In the cmd window, navigate to the drive letter from the previous step. Run the following command: Setup /PrepareAD /IacceptExchangeServerLicenseTerms - once complete move to the next step.
4. Run next command
From the same CMD window, run the last command: Setup /PrepareSchema /IacceptExchangeServerLicenseTerms and when complete, reboot your Exchange Server.