Restoring a plugin to its default state.

How do I reset a plugin to its default state. I was experimenting and made some changes and want to start over. I deactivated and re-activated, removed it from the plugins folder, re-added the plugin, and I don’t know what else to do. I’m guessing it has something to do with the database maybe? When I re-added the plugin to the folder, the stuff I changed was still there. Any help would be greatly appreciated.