Forms vary, but it's usually in the upper left, either between the payer and recipient addresses, or above them.
DFAS issued some of their initial 1099-R forms with the Payer's TIN/(FIN) missing a digit, they are mailing out new ones with the number corrected .
"Note: 2020 Retiree IRS 1099-Rs mailed in early January contained a Payer's Federal Identification Number (FIN) that is missing the last digit because of a printing error. The correct Payer's FIN is: 34-0727612. We apologize for the inconvenience."