You cannot file a prior year's W2, along with this year's tax return. You must file it by amending that year's tax return. There is a time limit on amending the return. You have three years from the date you filed your original tax return or two years from the date you paid the tax, whichever is later.
If you need directions on filing an amendment, please view the Turbo Tax FAQ below.
https://ttlc.intuit.com/replies/3288565
