You just need to amend your Form 1040 to Form 1040NR.
Here are the steps:
You would need to submit both the Form 1040-X and Form 1040NR together:
- Download the Form 1040-X from the IRS website (see below). On the front page of Form 1040-X, enter your name, current address, and social security number (SSN) or IRS individual taxpayer identification number (ITIN)
- Do not enter any other information on page 1.
- Do not complete Parts I or II on page 2 of Form 1040X.
- Enter in Part III the reason why you are filing Form 1040X.
- Complete a new or corrected Form 1040-NR. As TurboTax does not support nonresident forms, click here Sprintax.
- Across the top of Form 1040-NR, write “Amended”
- Attach the new or corrected return (Form 1040NR) to the back of Form 1040-X.
https://www.irs.gov/pub/irs-pdf/f1040x.pdf
https://www.irs.gov/pub/irs-pdf/i1040x.pdf, page 7 under Residents and Nonresidents
