Reduce the length of a group discussion

Is there any way to reduce the length of a group discussion without canceling it entirely and resubmitting a shorter time? I scheduled, as a tutor, a one hour group discussion which now has one student in it. I decided to schedule a 15 minute session as a student in the latter part of the hour. I was able to do it but I then I couldn’t find a way to shorten my teaching hour to accommodate my learning time without canceling, which I don’t want to do since I have a student.

Anyway I have edited the discussion description to limit the number of students so there should be no conflict.