First, start by booting your Windows 10 installation into the setup by changing the boot order in your BIOS to take priority with the CD, or use the ISO as a startup disk instead.
You’ll need to boot from Windows 10 installation media to do this. First, you’ll need to create Windows 10 installation media on a USB drive or DVD. Once you have, change the boot order on your PC and boot from the USB drive or disc.
Once the setup begins, hit Shift+F10.
This will bring up a command prompt. From here, we’re going to use the command prompt to replace the Utility Manager at the login screen with cmd.exe with the following commands:
move d:\windows\system32\utilman.exe d:\windows\system32\utilman.exe.bak
copy d:\windows\system32\cmd.exe d:\windows\system32\utilman.exe
Once this is complete, use the command “wpeutil reboot” to restart the machine.
After you’re back at the login screen, click the Utility Manager. If everything went right, you should see a cmd.exe.
This is the prompt you’ll use to create a new administrative user from the login screen. Type in the following commands, replacing <username> with the name you’d like to assign to the new account (no carrots).
net user <username> /add
net localgroup administrators <username> /add