Unfortunately, if you have already e-filed your return it is too late to add the W-2 you just received. Once you transmit your return you cannot change it or get it back. In order to add this W-2, you would have to amend it once the amended forms are available.
If you need to amend your return and you're amending to claim more money, the IRS says to wait until you've received your original refund before filing an amendment. Once you've received your original refund, feel free to cash or spend it while your amendment gets processed (this can take 12–16 weeks). 3 weeks after you mailed your amendment, you can start tracking its progress at the IRS Where's My Amended Return? site.
More information regarding amending a return can be found below:
https://ttlc.intuit.com/replies/3288565
