Trace the ingredients back to the meal
Mark which ingredients belonged only to the canceled dinner and which appear elsewhere. If the risotto is canceled, mushrooms might go while onions remain for soup. Count the new quantities rather than dropping an entire category. Two onions for two dishes may become one onion for the remaining dish.
Handle purchases that already happened
If the ingredients are already purchased, choose a real second use rather than leaving the old dinner on the calendar by default. Put mushroom sandwiches on tomorrow's menu, for example, and note whether that change removes another grocery item too.
Look at the ingredients now at home and choose an actual use, such as mushroom toast for lunch. Cross out the ingredients that lunch replaces from the shopping list. If there is no realistic second use, do not put a fictional meal on Friday just to make the original purchases look planned.
Tell the people affected by the change
A canceled dinner can affect the shopper, the cook, and someone who expected a portion for lunch. Send a short update such as “No Thursday risotto; mushrooms go into Friday lunch; keep the onion for soup.” If a delivery order is already submitted, check its actual change options before assuming the unwanted line can still be removed.