Missing Years- buying back only some years- How to identify the payment to HMRC

I want to make payment(s) for missing years. However I do not want to pay all the missing years. I sent the form CF83 in February 2023, completing the direct debit form to enable HMRC to deduct the payment from my UK bank account. I received a letter to say I should make the payment manually from my online banking. However when I make the payment how do I inform HMRC exactly which years the payments are for? The reason is the increase in pension from buying back missing years is not equal. As an example if I buyback 2017 my pension will only increase by £8 per year so spending over £800 is pointless. Some of the years have equal prices to buy back but do not have equal increase in my pension so I do not want the payment I send to HMRC being applied to years that bring me virtually no increase in my pension

Hi Paddy Murphy,
To make sure your payment(s) is allocated to the years you want it to be allocated to, you can either call the National Insurance helpline and tell the advisor what years you want your payment(s) to be allocated to.
Alternatively, you can send a letter to HMRC providing this information.
Please include your National Insurance number on your letter.
Contact details are shown below:
National Insurance Contributions and Employer Office
International Department
PT Operations North East England
HM Revenue and Customs
BX9 1AN
Telephone number – 0300 200 3500 or +44 19 1203 7010 if calling from abroad (Lines are open from 8am to 6pm Monday to Friday)
Thank you.