Can you check for a supposedly duplicate tx return

[SusanY1]

You can check to see if there is a full tax return on file by taking a look at your IRS Transcript, found here: IRS Transcript. 

If you are receiving an e-file rejection due to a duplication of your social security number, there is no workaround for this and the return must be filed by mail unless you are a dependent on another person's return (see below).

If your IRS transcript shows a full return that contains information that does not belong to you, then you may also want to file Form 14039 with your tax return.  

If there is no return on file the most common two reasons this tax year for the reject message are:

• you are listed as a dependent on another taxpayer's return (in this case, you may be able to e-file by indicating that you are claimed as a dependent on another tax return, (if you were properly claimed.)
• you filled out the non-filers form to receive an economic impact payment.  This actually places a simple tax return on file for you and requires that you file an amended or superseding tax return by mail.

[Texas Roger]

What notification are you getting that leads you to believe there is a duplicate tax return? If an efile is being rejected, what exactly does the rejection message say?

[monicahartman]

 I filed two tax returns electronically by mistake.  How can I take one back?

[xmasbaby0]

It is impossible to e-file the same tax return twice.  One of those attempts will be rejected.  Or maybe both.   Wait for the email that tells you whether your e-file was accepted or rejected.