When property that is exempt from taxation, except as provided in Section 3.28.015, has been erroneously assessed, or when improvements, which did not in fact exist when the tax became a lien, have been erroneously assessed on real estate, the council may, upon satisfactory proof thereof, with the written consent of the city attorney, and by an order entered upon its minutes, direct the tax collector to cancel such assessment; and if real property has been sold to the city for nonpayment of the taxes levied on such property or improvements so erroneously assessed and a deed therefor has been issued to the city, and the city has not disposed of the property so sold, the order of the council shall also direct the county recorder to cancel the deed so issued, so far as the same relates to such exempt property or nonexisting improvements. (Prior code § 6.04.890)