If you requested to have federal income taxes withheld from your Social Security benefits, you had to provide the Social Security Administration a Form W-4V, Voluntary Withholding Request.
See this SSA site for information - https://www.ssa.gov/manage-benefits/request-withhold-taxes
When you received the form SSA-1099 for your annual benefits statement, any federal tax withheld would be entered in box 6 of the form.
