Dad's laptop needs a full reinstall of Windows 11 Home. Where can I download a free copy?

He did some stuff that messed up his computer and I want to do clean install of the exact same Windows back onto it. Since the laptop came with Windows, I'm assuming he doesn't have to pay for a copy. (I'm a Linux/Mac guy) I'm not sure if there's a virus on the laptop, so I'm going to make the installer from my Debian computer.