Locally you can do that by deleting the content inside your deployment / data directory. A new database will be created when you start your app again. The very quick way is to delete your whole deployment directory.
If you want to delete data in your Free node it is faster to create a microflow that removes all your data. It would be nice if there was a simple method tho clean your free node of data. If you have a paid license it is easy again because there you can clear an environment.