The current Export Amendment (C81) form has been replaced. As detailed in previous communications the new form is now the only accepted method of submitting amendments.
The new online service is available on UK Trade Info. All supporting guidance on GOV.UK has been updated.
If you have any questions or cannot submit electronic forms, please contact us on 0300 594231.
https://www.uktradeinfo.com/trade-data/notice-of-amendment-to-an-export-declaration-c81