Find each arrangement that depended on the cancelled event
Write the cancelled activity in the middle of a small note and list what existed because of it. A Thursday class might have reserved the car, moved dinner earlier, required another adult to collect a child, and prompted someone to pack a bag. Review those items individually. Some can disappear; others, such as a care duty, still exist but may need a different owner. Removing one calendar entry cannot communicate all four effects.
Let the people who prepared for the event know
Ask whether the newly free time should stay free. One person may want to catch up on chores while another expected a quiet evening. Make that a fresh choice; the cancellation itself does not commit anyone to replacement work.
Check before spending the recovered time
The driver may already be on the way, the host may have bought food, or someone may have arranged an evening off work. Ask what has already happened before proposing a replacement. If the family wants a short meal together, agree on a time and who will attend. Otherwise restore ordinary arrangements and let the time remain unclaimed. The cancellation releases an activity; it does not automatically release a person from every separate duty around it.