Reset the current notebook
You can always return to the original course version through the File → Reset to original menu.
you will reset the whole notebook and therefore you lose your modifications on it . In most cases it is fine, for example lesson notebooks contain no change or very small changes. For exercise notebooks, think a bit before doing this!
Reset all the notebooks
The File → Reset all to original menu allows you to reset to original version all the notebooks of the Mooc .
if you do this, all your notebooks, except the notebooks used for wrap-up quizzes, will be reset. So think hard before doing this!