Anytime you buy a used PC you should do a clean install of Windows. This way you're not 'inheriting' any problems the unit may have had with the existing OS, and it also guards against any malware or viruses that might be on it, whether intentionally or unintentionally by the seller. With the GK3 Plus, however, you should use the system that's available
here. Granted, it's version 22H2, so you'll probably want to do an upgrade to at least 23H2, as 22H2 support ends on Oct 8th of this year.
Hopefully they'll have a 23H2 version of the system available soon, or even 24H2, so people won't have to worry about the upgrade afterward.
Having said this, if you're familiar with doing a clean install of Windows using USB installation media you've made with Microsoft's Media Creation Tool you can do that, but before doing so I'd make sure to first glean the Windows Product Key on the unit and write it down for that "just in case" scenario, as well as downloading and having the Drivers on hand, as you'll likely need a few after the Windows install. If you use the first method, as in the system available on the linked page, it already includes the drivers preinstalled, though some of them will likely update afterwards via Windows Update.