First step right click open Powershell with administrator.

Windows Server 2019 Evaluation
Windows Server 2019 Evaluation

Step 2 : Enter the command “DISM /Online /Set-Edition:ServerStandard /ProductKey:N69G4-B89J2-4G8F4-WWYCC-J464C /AcceptEula“.

Will process convert to full version and press Y. System will restart pc and open powershell again.

last step : “DISM /Online /Get-CurrentEdition” & complete convert to full version.