repeating parts of the course

Now that I am about half way through the course, I wanted to retake earlier lessons to fix these in my long term memory.
I cannot find a way to delete my previous answers. Can you help?

Just to the left of the green item (on the right) there will be a short 2-line comment: the top will says something like "100% Done", and underneath it will say "reset" in blue. Click on the latter and click "Confirm" to the dialogue box which comes up.
That's what I use when revising previous modules anyway.

Regards,
Pete