The only advice I can really give on this, is ask the person who edited it, sorry.
To edit an invoice locked by a VAT return, you would need to roll the returns back. However, if they’ve been submitted to HMRC and the figures will change, specifically if you end up owing more than what has been paid, you may need to contact them. You may also find this guide useful.
There’s more of a guide on rolling back VAT returns here.