19 CFR § 10.3003 - Filing of claim for preferential tariff treatment upon importation.
(b)Making a claim. The claim is made by including on the entry summary, or equivalent documentation, the letters “CO” as a prefix to the subheading of the HTSUS under which each qualifying good is classified, or by the method specified for equivalent reporting via an authorized electronic data interchange system.
(c)Corrected claim. If, after making the claim specified in paragraph (b) of this section, the importer has reason to believe that the claim is based on inaccurate information or is otherwise invalid, the importer must, within 30 calendar days after the date of discovery of the error, correct the claim and pay any duties that may be due. The importer must submit a statement either in writing or via an authorized electronic data interchange system to the CBP office where the original claim was filed specifying the correction (see§§ 10.3031 and 10.3033).