How to Report Repaid Underpayment from P800 on Self-Assessment for 2022-2023?

I need to submit a historical Self-Assessment form for the tax year 2022-2023 to declare additional self-employment income. During this year, I was only registered under PAYE for my regular employment, not Self-Assessment. For 2022-2023, I received a P800 tax calculation, which showed an underpayment. I have already repaid this amount upfront. Now, I'm trying to figure out where I should report this repaid underpayment in my Self-Assessment form so that it is included correctly in the tax calculation for the year. I have already completed the Tax Return for my PAYE income using the figures from the P800 calculation and have also included the additional self-employment income. However, the Tax Calculation doesn't seem to account for the underpayment that I’ve already repaid. How do I properly report this repayment to ensure it is factored into the final tax calculation? Thanks for any help!

Hi infinitejest89,
The payment made for the P800 underpayment will not be shown on your Self Assessment tax calculation.
Once you have submitted the tax return if you contact HMRC we can then arrange for the payment to be reallocated to your Self Assessment account
Self Assessment: general enquiries
Thank you. 

Hi, I called the Self-Assessment line and they told me that they are separate from PAYE and that I would need to contact PAYE for a Tax Refund to claim back for the underpayment that I repaid. Does this sound correct?

Hi,
If you previously repaid a PAYE underpayment in a specific tax year, and you then submitted a Self Assessment tax return for that same tax year, your overall tax liability for the year will be recalculated in Self Assessment, and the PAYE underpayment cancelled.
If you are then underpaid in Self Assessment, contact the PAYE department to transfer your PAYE payment to your Self Assessment record. If you are overpaid in Self Assessment, or you have already paid your Self Assessment underpayment, contact the PAYE department to have your PAYE payment refunded. 
Income Tax: general enquiries
Thank you.