In cases of any omission, mistake, defect, or irregularity in the preliminary proceedings on any special assessment in a city of the first class, the city council shall have power to correct such mistake, omission, defect, or irregularity, and levy or relevy, as the case may be, a special assessment on any or all property in the district, in accordance with the special benefits received and damages sustained to the property on account of such improvement as found by the city council sitting as a board of equalization. The city council shall deduct from the benefits and allow as a credit, before such relevy, an amount equal to the sum of the installments paid in the original levy.