We’re fans of AppCleaner as an app uninstaller, but over on How-To Geek, they point out that the free software is also useful for resetting apps back to their default state.
All you need to do is download and install AppCleaner, then search for the app you want to roll back to its default state. This means you’ll remove any settings, data, and login info. When you select the application you want, a popup with a list shows up. Here, unselect the actual application file, then remove everything everything else. This deletes all the app’s various settings so its restored back to its default. You can do this manually by clearing out specific files in your Library folder, but AppCleaner makes the process a bit simpler. Head over to How-To Geek for a more detailed guide.
How to Reset Any Mac App to Its Default Settings | How-To Geek