From the hmrc website…
Reduce your payments on account
If you know your tax bill is going to be lower than last year, you can ask HM Revenue and Customs (HMRC) to reduce your payments on account. Either:
log in to your online account and click ‘Reduce payments on account’
send form SA303 to your tax office
HMRC will send you a refund if the payments on account you’ve made are higher than your tax bill.
However, with it being nearly mid-July now it might be a little late for that to all go through before the 31st. It may be difficult now but the bonus is you’ll probably be due a rebate in January and the amount owing on your first payment for the next year will be lower.
IANA (fully trained) accountant. Although this has highlighted a bit of a hole in my knowledge for my exam on Wednesday ha!