@prince-xyryl Apologies for coming across harshly - I don’t see why you can’t delete an account. The steps I gave you below is (generally) how I’ve been deleting accounts for a decade - since Windows XP. Again, this isn’t a FOG issue and the problem is probably better suited for a Microsoft troubleshooting forum. They will probably want to know what OS you are using.
It sounds like you’re using SysPrep, and it sounds like your unattend file is not working in the way you’d like - because you’re getting the OOBE. Yes, you can create an account prior to uploading. And you can also set that account as the default account that is auto-logged into. But I am not sure if sys-prep will undo that work or not.