19 CFR §10.235

1. (a)Declaration. In connection with a claim for preferential tariff treatment for an article described in § 10.233(a)(1) through (5), the importer must make a written declaration that the article qualifies for that treatment. The written declaration should be made by including on the entry summary, or equivalent documentation, the symbol “R” as a prefix to the subheading of the HTSUS under which the article in question is classified. Except in any of the circumstances described in § 10.236(d)(1), the declaration required under this paragraph must be based on a complete and properly executed original Certificate of Origin that covers the article being imported and that is in the possession of the importer.
2. (b)Corrected declaration. If, after making the declaration required under paragraph (a) of this section, the importer has reason to believe that a Certificate of Origin on which a declaration was based contains information that is not correct, the importer must within 30 calendar days after the date of discovery of the error make a corrected declaration and pay any duties that may be due. A corrected declaration will be effected by submission of a letter or other written statement to CBP, either at the port of entry or electronically.