Tax act- I filed taxes online with them, already got return. Can I still file a form 8379 (injured spouse)?

If you did not include in the efile, you print it, sign it and mail it with copies of the W-2s to your IRS service center.

You do NOT include a 1040X. That would simply delay it further.

If you don't have children and didn't claim any credits, then yes, the IRS looks at what each of you would have paid separately to determine what your share is on the 8379. However, it's too late to file the 8379 form to get "half" of the stimulus back. The IRS says to allow 8 weeks to process the form and if it's not processed within the the next 2 weeks, it will be too late for the IRS to get retreive the money and issue you a check before 12/31.

You filed on-line and it was accepted...I am presuming that is the question.

Yes, you can still file the 8379, but it will now have to be an amended return (1040X) and paper filed.

You will have to do it on paper and mail it in if you didn't include in your original filing.