You can skip the checksum verification. It's used to verify if the downloaded ISO image was downloaded without errors. Fedora Media Creator downloads the ISO a runs the check automatically so you don't need to verify the checksum manually. But if you really want to, there should be Fedora-Workstation-Live-x86_64-25-1.3.iso file in your Downloads folder (on Fedora/other Linux distro; don't how this works on Windows).