If the taxpayer shall make any error in computing the tax assessable against him, the City Clerk shall correct such error or reassess the proper amount of taxes, and notify the taxpayer of his action by mailing him promptly a copy of the corrected assessment, and any additional tax for which such taxpayer may be liable shall be paid within ten days after the receipt of such statement. If the amount already paid exceeds that which should have been paid on the basis of the tax so recomputed, the excess so paid shall be immediately refunded to the taxpayer upon the request of the City Clerk and shall be payable out of any funds available for the purpose. The taxpayer may, at his election, apply an overpayment credit to taxes subsequently accruing hereunder.