I am an international student. I used Turbotax in the past three years for filing my taxes. I recently realized that I can't do that. How can I correct this?

As an F-1 visa holder, you are considered as a nonresident for five years from the year you first enter the US (2013-2017).  From January 1st, 2018, if you stay within the US more than 183 days, you are a resident.  Therefore, you can use TurboTax to file 2018's taxes.  

As far as the past three years' taxes, if you have filed a Form 1040 with TurboTax, you would need to amend your taxes to file a Form 1040NR.  On Form 1040NR, you would report any of your US source income.  You need to submit both the Form 1040-X and form 1040NR together:

• Download the Form 1040-X from 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 the 1040-NR, write “Amended”
• Attach the new or corrected return (Form 1040NR) to the back of Form 1040-X and submit to the IRS.
• https://www.irs.gov/forms-pubs-prior-search?search=1040x (Prior year's )

You cannot e-file but only paper-file.  Print out the tax forms and submit them by mail. See instructions of Form 1040-X.