You can adjust the details of your plan anytime under Plan → Manage your plan:
Paces: make your training paces easier or harder.
Goal time: update your target race time. Your paces recalculate around it.
Longest run: set your realistic current longest run so we build from the right starting point.
Runs per week and long-run day.
Intensity and how many hard sessions you want.
Unavailable days, distance unit, and more.
Change what you need and your plan updates automatically.