It is best to just empty the box and dispose of the old nest after the young have fledged. Put the old nest in a trash can. Don’t trash it near the nest box. I usually take the nest box off the pole and clean it with soap & water. Let it dry for a couple of days and then return it to the pole. The birds usually revisit the box after a week or 2 away with their brood.
David
Stafford, VA