You would need to file Form 8379 within 3 years
from the due date of the original return
(including extensions) or within 2 years from
the date that you paid the tax that was later
offset, whichever is later.
Since you have already e-filed your tax return you would file the Form 8379 separately by mail, please
be sure to attach a copy of all Forms W-2
and W-2G for both spouses, and any Forms
1099 showing federal income tax
withholding, to Form 8379.
The processing
of the form may be delayed if these forms
are not attached, if the form is incomplete
when filed, or if you attach a copy of your
joint tax return.
Here is an IRS link to the Form 8379 filing instructions: https://www.irs.gov/pub/irs-pdf/i8379.pdf.
Here is a link to the Form : https://www.irs.gov/pub/irs-pdf/f8379.pdf.
The following link will provide the mailing address to mail the form: https://www.irs.gov/uac/where-to-file-paper-tax-returns-with-or-without-a-payment.
