When I do a course challenge and get something wrong, I end up somewhat annoyed because I cannot restart. I have checked, and it appears that similar sentiments inspired the addition of the start over button two years ago. However, at that time, it was said that it was still being worked on for course challenges. As it has apparently been in the works for two years, I would like it very much if it were added. While I understand that the Khan Academy team is likely very busy with adding other features(The app dark mode is really nice), I hope that this can be added.