I've read IRS will accept that , but there's no reason to do it that way.
The correct way:
get Form 1040-X from IRS website and mail it in with your 8938, which you can also get in fillable PDF.
Note: since you are not changing any dollar amounts on your amended tax return, you can leave all the lines 1-23 EMPTY.
Part III explanation: "didn't include Form 8938 with e-File".
You will have to mail it so this does not use up your one 1040-X e-File.
