If you mistakenly filed a Form 1040 U.S. Individual Income Tax Return and you need to file Form 1040-NR U.S. Nonresident Alien Income Tax Return, or vice versa, you will need to amend your return.

Per IRS Instructions for Form 1040-X Amended U.S. Individual Income Tax Return, page 2:

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

To amend Form 1040NR, 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 1040-X.
• Don’t enter any other information on page 1. Also, don’t complete Parts I or II on page 2 of Form 1040-X.
• Enter in Part III the reason why you are filing Form 1040-X.
• Complete a new or corrected return (Form 1040, 1040-SR for amended 2019 and later returns, 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 1040-X.

Per IRS Publication 519 U.S. Tax Guide for Aliens, page 37:

Amended Returns and Claims for Refund

If you find changes in your income, deductions, or credits after you mail your return, file Form 1040-X, Amended U.S. Individual Income Tax Return. Also use Form 1040-X if you should have filed Form 1040 or 1040-SR instead of Form 1040-NR, or vice versa.

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