This situation is referred to as a Claim of Right under IRC Section 1341. It can be claimed as either an itemized (miscellaneous) deduction or as a credit if the amount repaid is more than $3000. The deduction is the simpler way to claim your repayment, but a credit might save you more money.

To claim the repayment as an itemized deduction, you would use TurboTax Online Deluxe or a higher version.

1. Click on Federal Taxes on the left side of your screen.
2. Click on Deductions and Credits.
3. Select All Tax Breaks, and scroll down to Other Deductible Expenses.
4. On Did you have any of these less common expenses? say Yes.
5. If your repayment was less than $3000, enter the amount and description on the screen Tell us about your less common expenses
6. Continue to the screen Did you have any of these other deductions? If your repayment was more than $3000, answer yes.
7.  Enter the amount on the next screen.

If you decide to claim your repayment of over $3000 as a credit, follow the information starting on page 33 of IRS Publication 525 Taxable and Nontaxable Income under Repayments. This requires a special computation, and you would need to use a Desktop version of TurboTax and enter your credit using the Forms mode. Also see this answer for more information.

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