Hi Philipp, as far as I know, there is no way for us to reset our progress in learning paths.
Nevertheless you can always go back and open a learning path again and read through the single chapters and modules again.
If you just want to read and learn again, this should not be a problem
Also, you can create a new app to practice from scratch. Especially if you've applied security in the previous app, your learning effect will be better if you start over again!