You can only delete a VAT Return when it's a draft (not submitted to HMRC) or when your VAT submission has failed.
This can happen if you register for Making TAX Digital (MTD), and select Submit to HMRC by other means by mistake.
To resolve this, you’ll need to resubmit the VAT Return.
Read resubmit a manual VAT Return with Making Tax Digital (MTD) for more guidance.
If you can't delete a journal, you can reverse it. Read how to reverse a journal for more guidance.