One off pension contribution - how to inform HMRC?

Last year (tax year 22/23) I worked for part of the year before being made redundant. All my income came from the one employment, and I paid tax via PAYE. I was in a workplace pension with tax relief claimed via my payroll. After being made redundant I consolidated my pensions, and made a one-off top up payment of over £10k. At the moment HMRC don't know about it as the pension company didn't tell them and have said I need to do so. HMRC have already done my calculation and sent me a refund cheque based on their calculation without knowing about the pension top-up. How do I get relief for the pension top-up? Do I need to do a self assessment, or can I just tell HMRC about the one-off payment so they can recalculate for me?

Hi

If you are required to complete a self assessment tax return, this pension payment would be declared in box 1 of page TR4 on the SA100 tax return.  
If you do not need to submit a tax return, you will need to write to:
H.M. Revenue and Customs
Pay As You Earn
BX9 1AS,
claiming personal pension relief and providing supporting evidence from your pension provider of the payment that was made.

Thank you