I've overpaid HMRC for VAT. I have assigned the payment to the return and the balance is showing (-£5,436) on the return screen. How do I allocate this to another return?

Hi louisepenberthyj, thanks for reaching out to us here on the Community. Was the whole payment relating to that specific return and the previous returns?  

The payment was matched to a single VAT return.

I made an extra payment to HMRC by accident. I matched that overpayment to the next VAT return and it gave me a balance of -£5,436. I want to apply this balance to the next 2 VAT returns, how do I do this?

Thanks luisepenberthyj, when you record the overpayment against the original VAT period this will automatically deduct the difference (overpayment amount) from the total VAT due amount on your current open return. When you click record payment on your next return this will then show the VAT due for the period and total VAT due, the second amount will take into account the over payment.