I decided to add a B race to the same day one of the PlanBuilder’s workouts was scheduled.
When doing it, it asked whether I wanted the plan recalculated. Without knowing the consequences I said yes.
Unfortunately it has totally screwed up all of the following workouts and moved everything forwards!!!
My original slightly tailored planbuilder said:
Monday - workout
Tuesday - workout
Thursday - workout
I wanted to change the Tuesday workout for a B race. Now it says:
Monday - nothing
Tuesday - B race
Thursday - workout
So it has eliminated the workout before the B race, eliminated the workout on the same day as the B race and looks like it left Thursday the same.
I haven’t looked enough to see if it has changed anything else, all just because I added a B race. 
How do I undo this?
Also, how can I add other races without it automatically changing a previous training schedule?
Thanks.