When an event is pushed back by 2 weeks how should I treat the 200mgg plan when it ends

Like many people my key events have been moved part way through a plan.

A key 177 mile hilly event has been moved from 8 May to 22 May. I am well into the 200mile gravel grinder plan which was scheduled to finish for original 8 May event date.

To make use of the training I am riding with friends a practically flat 170mile route on the 8th May.

What’s best approach to fill in the schedule from 9th May to the hilly 177miler on 22 May?

I would probably delete the original plan and then re-apply it to end on the revised event date. So you will then effectively repeat the last couple of weeks of your current plan, but preserve your final build and taper.