Hi Rgl21, thanks for joining the Community
To delete the payment, find the transaction in your All sales list (Take me there) and from the Action column, select the small arrow ▼ icon and then Delete.
Changing or deleting a transaction that has been filed in a previous period will automatically create a VAT exception in the open VAT period. To view the VAT exception, go to Taxes and select VAT. In the Action column, select the dropdown arrow next to the VAT return and Select View exception details.