Exports are zero rated, so should be reflected in box 6. See section 3.7 of notice 700/12: https://www.gov.uk/guidance/how-to-fill-in-and-submit-your-vat-return-vat-notice-70012#section3
Supplies to the EU from NI are shown as a separate bullet point on section 3.7 because they’re not technically “exports”, they’re called “dispatched” instead – see sections 2.9-2.10 of the same notice.