1. Run command line as Administrator and run command for your version of OS:

Windows Server 2016
dism /online /set-edition:ServerStandard /productkey:WC2BQ-8NRM3-FDDYY-2BFGV-KHKQY /accepteula

Windows Server 2019
dism /online /set-edition:ServerStandard /productkey:N69G4-B89J2-4G8F4-WWYCC-J464C /accepteula

Windows Server 2022
dism /online /set-edition:ServerStandard /productkey:VDYBN-27WPP-V4HQT-9VMD4-VMK7H /accepteula

Wait when process ends.

2. Restart.