If you want to restart a plan from the beginning, you can simply stop the plan and then restart it.
Here's how to do that on the web and apps:
Restarting a Plan from the Web
1. Open up My Stuff -> My Workout Plans.
To stop following a workout plan, go to the "My Stuff" tab of your Dashboard and then navigate to "My Workout Plans" on the left side of the page.
2. Hover your mouse over your current plan and click "Stop Plan".
Locate the workout plan that you want to stop following. Hover over the workout you would like to stop following. Click "Stop Plan."
3. Locate the plan under "My Recently Followed Workout Plans and restart it.
Restarting a Plan on the Apps
1. Tap your profile image to open the "My Profile" page.
2. Tap the plan shown in the Workout Plan section.
4. Choose the plan you want to stop, then tap "Stop" in the top right corner and confirm on the pop-up message.
5. Tap the "Start" button to restart the plan.
6. Tap "Start Plan" at the bottom of the page to confirm and restart your plan.
Now you can start over from the beginning!