The only way to change/correct a previously filed tax return that has been accepted by the IRS is to amend it. People amend tax returns to add income or make changes that affect the amount of taxes owed or refunded. However, to just switch valid social security numbers would not necessitate an amended tax return. The IRS would have notified you if they saw a problem with your previously filed tax return. I would make sure that you use the correct social security number next to the correct dependent moving forward.