Help with rescheduling a workout on calendar

I was down to the last day of a workout program on my calendar, but life interfered and I wasn't able to do my workout on Monday or Tuesday. This morning, when I went to reschedule the day and push it forward, the "reschedule day" option is greyed out, I know the workout is in the past, but shouldn't I still be able to reschedule it? Any idea what I might be doing wrong?