nkit to iso

System: GameCube

I'm trying to convert a gamecube nkit.iso to an iso so i can apply a patch. However, when extracting the download, all I get is a compressed file, either winrar or 7z, and when I click to open it, I just get a message that says "the archive file is either in unknown format or damaged". I've tried to open it with either winrar or 7-zip, and I've even dragged the nkit.iso into the NKitProcessingApp and selecting "convert to iso", yet the result in the processed folder is just a winrar or 7z file that has the same message "the archive file is either in unknown format or damaged" when I click on it. How do I get the iso file so I can apply the patch?