People buying used iPods typically will restore them after they purchase them if you keep your music on it, from my experience. Up to you what you want to do, of course.
Plug it into a computer with iTunes (PC or Mac running Mojave or earlier) or Finder (if it's running macOS Catalina or higher). There is a restore option when it's plugged in, and after you restore it, it will have removed all songs, settings, and other things that were synced. There was not a 1st gen iPod with 80GB. You likely have a 5th or 6th gen. You can find what exact iPod model you have here:
https://support.apple.com/en-us/103823