How do I amend my already filed tax returns to include 1040NR form?

I've recently filed for my tax returns for 2017 with Turbo Tax. I wasn't however aware that since I am an international F1 student, your app didn't handle my case. I heard that I'm also supposed to file my 1040NR form. I'm a little worried, since my tax refund has already been 'approved'. I haven't received it yet though.

Could you please advise me on the best way to handle this?

Thank you!