I've already e-filed using TurboTax and both returns were acccepted. I later received a W2 from an employer from which I had forgotten that I did some work for early in the tax year. What should I do?

[DoninGA · Accepted solution]

Do NOT change anything on the return that has been filed. 

If the IRS accepts the return, then you must wait for the tax refund or the taxes owed and paid to be processed.  You would then have to file an amended tax return, Form 1040X, to add the W-2 to the accepted tax return.  An amended federal tax return can only be printed and mailed, it cannot be e-filed.  The IRS will take 16 weeks or longer to process the amended tax return.

See this TurboTax support FAQ on amending a 2016 tax return - https://ttlc.intuit.com/questions/3061514-how-do-i-amend-change-or-correct-a-2016-return-with-turbot....