I am international student who filed tax return with turbotax.How can I amend that tax return which is already filed since Turbotax dont support international students.

It depends but if you will not be able to "cancel" an accepted US income tax return if it was efiled.

If you are a nonresident alien and should have filed a 1040NR, then you will need to file an amended return (Form 1040X).

Here are the steps to file an amended return when you filed a 1040 but should have filed a 1040NR:

1. Download a copy of both the Form 1040NR (which is not supported by TurboTax) and Form 1040X
2. On page one of 1040X, just enter your name, current address and your social security number (SSN) or IRS individual taxpayer identification number (ITIN) but no other information
3. On page two of 1040X, do not complete Parts I or II but in Part III (the explanation section), enter your reason for filing an amended tax return (such as "filed Form 1040 when I needed to file Form 1040NR.)
4. Complete your Form 1040NR and write "AMENDED" at the top of page one
5. Attach a copy of both your 1040NR and your 1040 (as filed) to the back of the 1040X.
6. Mail the all copies to the IRS.

thank you