1. Launch Sconfig.cmd
When you open your Windows 2019 Server, you will be presented with just a command prompt. Type in sconfig.cmd and press enter
2. Select an Option
Select option 1 to join the domain, type in 1 and press Enter.
3. Select D
You will now be asked if you want to Join a Domain or Workgroup, type in D and press enter
4. Provide domain name
At the next prompt, type in your domain name, in this example I used tlab.local
5. Enter Credentials
Enter in the account that has rights to join a machine to the domain in this format: Domain\username, once done press enter and a new window will appear for you to type in your password. Once done press enter again.