Changing end date of training plan over half way through the plan

I need advice on how to salvage my training plan. Im doing a low volume century plan that started off well in early February. Then some real life crisis interrupted it from week 8 through 13 and I got little riding in at all. I restarted in week 14 but I am still having difficulty in getting all workouts done as scheduled. The specialty phase is supposed to start next week but I decided to put off my century ride from September 11 until sometime in late October. There will be a week in that time when I won’t be able to train at all. I’m not sure how to change the end date of the plan without starting all over. I’m unsure if I’m ready for the specialty phase considering all the workouts I’ve missed. Any advice would be appreciated. Thanks.