So I duplicated a lesson and taught it.
When I wanted the students to go back to a previous task I used the "focus" button, but this did not work (probably due to poor wifi at the time?).
Instead I tried telling the students which task I wanted them to look at, only I did not have the same numbers as they did. I had ten tasks and they had eight (as I had chosen not to send two).
Other than the fact that the focus button should have worked, what can I do if this happens? Can I number the tasks myself? Can I see the students' number so I know which task is number x for them?
Today I solved this by looking over a student's shoulder, which of course works so perhaps no other solutions are needed, but still, if anyone has a better suggestion.....?