Here is a notice posted on the 2021 Harmonized Tariff Schedule. Except as noted there is no need to toggle between HTS codes for imports and Schedule B codes for exports. Exporters may use HTS codes in place of Schedule B. Go to https://hts.usitc.gov/current and choose the view tab.

Harmonized Tariff Schedule of the United States (2021)
Annotated for Statistical Reporting Purposes

NOTICE TO EXPORTERS
Through this notice, this HTS publication may be used in place of the reporting codes of Schedule B for reporting exports on the Shipper’s
Export Declaration or under the program for electronic reporting of exports. Except as noted below, the statistical reporting numbers (with
the article descriptions and units of quantity) for articles falling in Chapters 1 through 97 may be used in place of those in Schedule B. The
special prefix symbols which denote special tariff treatment should not be included. The following provisions are applicable for export
reporting purposes in lieu of the corresponding provisions in the HTS:
Description S

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