We do not currently have a way to reset the progress on our sequential programs (such as the 7 Days of Calm), and we apologize for the inconvenience. We recognize this is a much-needed feature, and hope to make it available soon.
In the meantime, you can track your progress when repeating a program by checking your Session History to see which session was most recently completed. You can access your Session History by, first, tapping the "More" button in the bottom right corner of your Calm app and then tapping "Profile." On your profile, tap "Calendar & History" to display your session history.