If you're currently in the middle of a training plan, select your Start Date as the day you started your current season of training.
How to Build a Plan if You've Already Started Training
From the TrainerRoad Calendar, check when you started training this season.
When building your plan with Plan Builder, select your Start Date as the first day of training from this season, not the date you're building your plan.
For example, Today's date is December 16th, 2019. My training season began on November 25th. When adding my new custom plan, I set my start date to November 25th.