"(c) Federal reserve system gold certificates.—Not later than 180 days after the date of enactment of this Act, the Federal reserve banks shall tender all outstanding gold certificates in their custody to the Secretary. Not later than 90 days after the tender of the last such certificate, the Secretary shall issue new gold certificates to the Federal reserve banks that reflect the fair market value price of the gold held against such certificates by the Treasury, as of the date specified by the Secretary on each new gold certificate. Upon issue by the Secretary, each Federal reserve bank that receives a new gold certificate shall remit the difference in cash value between the old and new gold certificates to the Secretary for deposit in the general fund within 90 days."
https://www.congress.gov/bill/118th-congress/senate-bill/4912/text