No, you can file Form 8379 with your joint tax
return or amended joint tax return (Form
1040X), or you can file it afterwards by itself.
File Form 8379 with Form 1040X only if you
are amending your original return to claim a
joint refund.
To file it by itself, then
If, you are amending to change your filing status to Married Filing Jointly, then you can add Form 8379 too. See
FAQ below for more info on amending: https://ttlc.intuit.com/replies/3288565
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