I know that there have many requests for a "Restart" button, but have been declined. However, if someone wants to re-attempt the exercise, they will just click "Done" and click "Try again":

So isn't it the same if a "Try again" button is given as an option on this page:
While seemingly trivial, this will save some time, especially for those who have a hard time with a topic, as they might need to redo the exercise many times.