The IRS provides instruction in Publication 525, page 34 (https://www.irs.gov/pub/irs-pdf/p525.pdf). Note that they offer two methods for figuring your tax - it's possible that method 1 (using the amount repaid as an itemized deduction) isn't making your total allowed deductions greater than the standard deduction. There's an example in Pub 525 as well, and they give instructions for claiming a refund of SS and Medicare tax.
