VAT Error Question

[TRIPLEENTRY]

I have just realised that last quarter's VAT return I included £739.11 too much on the total of VAT reclaimed on purchases! Therefore I owe them this money. How can I correct this in my return for this quarter as my total of VAT on purchases this month is only £329.45. If I add the amount I owe on to VAT due on sales then the total value of sales (box 6) will not look right. Please help someone!! Many thanks.