After you file

If you filed a Form 1040 but were not a U.S. citizen or resident, you need to file a Form 1040X amended return with a Form 1040-NR attached. 

First, you will need to prepare a Form 1040-NR tax return.  SprintTax is a software that can prepare a Form 1040-NR.  Once you have prepared the Form 1040-NR, you can print and manually complete the Form 1040X at this link, using the instructions shown below (from Form 1040X at this link).

Resident and nonresident aliens.

Use Form 1040X to amend Form 1040NR or Form 1040NR-EZ. Also, use Form 1040X if you should have filed Form 1040 (or, for years before 2018, Form 1040, 1040A, or 1040EZ) instead of Form 1040NR or 1040NR-EZ, or vice versa.

To amend Form 1040NR or 1040NR-EZ, or to file the correct return, do the following:

• Enter your name, current address, and social security number (SSN) or individual taxpayer identification number (ITIN) on the front of Form 1040X.
• Don’t enter any other information on page 1. Also, don’t complete Parts I or II on page 2 of Form 1040X.
• Enter in Part III the reason why you are filing Form 1040X (e.g., filed Form 1040 instead of correct Form 1040NR).
• Complete a new or corrected return (Form 1040, Form 1040NR, etc.).
• Across the top of the new or corrected return, write "Amended."
• Attach the new or corrected return to the back of Form 1040X.

@AlexandraKaellner