If you want to adjust when your program start date, follow these steps:
Open the On-demand workout library
Tap Explore from the bottom left corner of your screen. Make sure Workouts is selected from the bottom menu.
Select your active program
This will be the program with Active tagged in the top left corner.
Update your schedule
Hit the Update schedule at the bottom of the screen.
Choose your start date and program day
Select the date you want to begin, then tap the pen icon next to “Start from Day 1” to choose which day of the program you’d like to start with. Tap Add to Schedule when you're done.
Your workout program will now be updated with the new start date.