You shouldn't need to amend your 2014 return.
Your employer is only supposed to amend the W-2 boxes for Social Security and Medicare. They are not supposed to amend box 1 for your taxable wages. That means you will not need to amend your 2014 tax return.
For your 2015 tax return, you need to go through the procedures of a "repayment" to get a deduction or credit on your tax return.
https://www.irs.gov/publications/p525/ar02.html#en_US_2014_publink1000229600
