You will need to amend the 2015 tax return that was filed using IRS Form 1040X and enter the military W-2 for 2015. An amended tax return can only be printed and mailed, it cannot be e-filed.
See this TurboTax support FAQ for amending a 2015 tax return originally completed using TurboTax - https://ttlc.intuit.com/questions/3410543-how-do-i-amend-change-or-correct-a-2015-return-in-turbotax
