The express waiver for Northern Ireland has been extended from March 31st to October 1st for business to business goods, there has also been a 6-month rolling extension for business to consumer and consumer to consumer goods from the date which guidance is published.
You can find the updated guidance on the below links:
Sending parcels between Great Britain and Northern Ireland
Apply for authorisation for the UK trader scheme if you bring goods into Northern Ireland
Check if you can declare goods you bring into Northern Ireland not at risk of moving to the EU