If you haven’t already downloaded it, here’s the link to do so: https://download.gimp.org/mirror/pub/gimp/v2.8/windows/gimp-2.8.18-setup.exe
Always be sure to download from the original official source, (which in this case is: “https://download.gimp.org“) Don’t download it from “free-gimp-download.com”, or any other such shady site, unless you’re willing to take the risk of infecting your computer with things other than editing software. 🙂