If you’ve entered an invoice or a journal incorrectly and in doing so the wrong amount has gone or maybe no amount has gone to the VAT account and in turn the VAT element has not appeared in your VAT return you can correct this very easily, two ways. The first is to reverse your original transaction using the Copy/Turn/Reserve options and then enter the transaction again correctly.
If you have more than one entry affecting the same account then instead of reversing a lot of entries a quick way to correct this is to create a journal, in this example the VAT element of £150.00 has been charged to the telephone account. In order to correct this and see it in the VAT Return create your entry as shown in the example below, this will credit the phone account with £150.00 and debit the VAT account along with appearing in your VAT return, making sure you change the VAT amount to agree with the total amount and the VAT code is blank against the contra account:-
And finally the telephone account shows the £150.00 crediting the account:-