I am an international student now working in the US. I should not have filed 1040ez but 1040nr. How do I fix this? Thanks.

To amend from Form 1040 to 1040NR,   here are the steps:

You would need to submit both the Form 1040-X and Form 1040NR together:

1. 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)
2. Do not enter any other information on page 1.  
3. Do not complete Parts I or II on page 2 of Form 1040X.
4. Enter in Part III the reason why you are filing Form 1040X.
5. Complete a new or corrected Form 1040-NR.  As TurboTax does not support nonresident forms, click here Sprintax.
6. Across the top of Form 1040-NR, write “Amended”
7. 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