If TurboTax deducted the total interest but you and IRS agree that only a fraction is deductible.
prepare an attachment that shows your calculation of the fractional part that is deductible and the part that is not deductible, based on rules in Pub 936 which you can reference.
you could supply an updated Schedule A.
If you interpret 936 correctly, IRs would accept that and make the necessary changes to your tax return.
OR, ask the IRS to do the calculation for you.
@grich01R
