When you are in an instance of a recurring project, you can view and/or modify the schedule. On the project Detail page you will see a button next to the project name with the schedule detail.  To modify the project schedule, click on the button.

The buttons may be different colors and each color represent the state of the project schedule:

Green is an active schedule

Red is a schedule that has passed it's end date

Gray is a project that has an inactive schedule