No, you do not have to attend the overview/orientation, but attending the overview will help ease the anxiety of the day of your ECERS review. The overview will give you an idea of what to expect on the day of the review.
The best thing for you to do is relax and try to keep your routine on the day of the review as normal as possible. The day of your review is probably not the best day to try a new routine.
You will begin to receive professional development support from the Early Education Support Provider once you have your first ECERS review. Your EESP will contact you to set up your first visit.