My wife received an SSA-1099 that includes a lump sum paid in 2018 for 2017. This sum (and more) was paid by LTD in 2017 and reported on our 2017 tax return as income. We paid this sum back to the LTD carrier. Turbotax deluxe lets us show the sum was for a previous year, but there does not appear to be a way to show taxes were already paid on this sum last year as income (not taxable SS payments). How do we avoid being taxed twice? The carrier pointed me to IRS-pub 915, but I how do I do this in Turbotax?
I suggest that you refer to the following answers, which were posted by TT for 2017.
https://ttlc.intuit.com/questions/4332060-help-with-2017-ssdi-lump-sum-award-and-repayment-back-to-p...
https://ttlc.intuit.com/questions/4321469-2017-ssdi-lump-sum-repayments-to-ltd-long-term-disability-...
These are answers to questions very similar to yours. If the above links do not work, look at your question and see the Similar Questions listed below yours.
Note however, that because of the change in Tax Laws effective in 2018, that the itemized deduction may not be attractive for your situation. Of course, that will depend on the specifics of your income and SSDI amount repaid. Be certain to check both the deduction and credit alternatives and choose the one which results in the lowest taxes to be paid.
Also note that the above links are targeted toward the 2017 TurboTax software. I am assuming that the 2018 TT process for Lump Sums has not significantly changed.