IRS has held my tax refund for 2021. I got the notice (CP05A) . 'Statement of benefits on retirement income....' How do I get it? Please provide contact and online links.

IRS has held my tax refund for 2021. I got the notice (CP05A) from IRS asking for three details for reviewing my tax return. I have first two. which is my payslips and detail about my employer.

I don't have information for  the 3rd question, Which I stated above. Appreciate contact, online link to get the detail.