You have selected an activity, made sure that it is suitable for the person and that it meets the requirements of a proper Montessori dementia activity. What next?
Of most importance is your mindset. You have to be ready to coach the person, observe how they handle the tasks involved, give them the time they need to complete the tasks, and celebrate their successes with them. If everything comes together, if your hard work pays off, you will be rewarded beyond your expectations with the moment of accomplishment that you will share with together.