Hello [NAME] Ashraf,   There is no documented steps on full OS default restore, therefore I'm unable to provide you an official step. Based on my experience, usually a restore is done from the backup which administrators do when they start working on the server. I would a link externally, but I am unable to verify that if it is a valid instruction: [URL]   From my suggestion, it would best to restore the OS by reinstalling it. 
I have purchased new Dell R740 server with Windows server 2019 Std. For some reason I have to reinstall/Reset Windows Server 2019 on same server. The installation is pre installed with license activated. Now is there any way to reset the server on factory default or I have to reinstall Windows Server 2019 with its media from OS deployment. Kindly guide me how to reset my server to default factory setting with OS.
How to reset preinstalled Windows 2019 server on R740