You don't enter the Flex Spending amount into TurobTax. The Flex Spending amount is deducted from your W-2 Box 1 Wages, Tips, Other Compensation amount, that is reported by your employer.
Part of a Flex Spending amount could be Dependent Care Benefits. They are reflected on your W-2 Box 10.
Related information: Plan now to Use Health Flexible Spending Arrangements in ... - IRS.gov
