How do I show my 1990's nondeductible IRA contributions on Form 8606 when they were transferred into my TIAA 403.b?

I moved all my IRAs to TIAA 403.b a few years ago. $12,000 were nondeductible from the late 1990s. I don't believe we mentioned the nondeductible funds when transferring. I converted $17500 to Roth last year. TurboTax asked if any of the funds were nondeductible (said yes due to the IRA funds), it takes the amount, but the deduction doesn't show up anywhere. How do I show those deductions. Do the deductions only work if they come from an IRA? Do I need to transfer money from the 403.b to an IRA to get the deductions? or ???? Thank You!

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