You need to get a IRS transcript of your account or ask them who the income is from. Then contract the issuer why they sent the IRS a 1099R. If it is legitimately yours they may have sent your 1099 copy to the wrong address. If it’s for an account of yours you might be able to log in and download a pdf of the 1099R.
Could be for many things. Like an old 401K account that was liquidated when you left that employer. Or did you roll over a 401K or IRA account to another account? Or convert it to a ROTH IRA? How old are you? If you are over 72 you need to take a RMD from your accounts. Maybe you forgot account an old account.