Underpaid tax from previous years

Hi all. I'm a PAYE earner who has recently registered for self assessment and completed self assessments for 21-22, 22-23 and 23-24. For both 21-22 and 22-23 I (my partner) received child payment benefits, and since I was over what was then the income threshold I will need to repay those payments for both of those years in full. This was identified by the calculator when filing online. Fair enough obviously, but with a payment of £3k or so due, paying this in the next tax year would be preferable to an immediate payment to HMRC. Is there a way my tax code can be changed to account for this, or will it be done automatically? Thanks in advance for any insight.

Hi,
For the balance to be included in the tax code the balance due needs to be less than £3000.
For 2021/22 it is now too late to include the balance in the code.
For 2022/23 to collect the underpayment through your code we must get your online return by 30 December 2023 and we must capture the return on or before 31 December 2023. 
Thank you.