I am an international student, back in 2017 I did not know that I need to file fax returns. But now I know, so, after I filed this year's tax return, I was told that although I did not file my last year's tax I can still do it. So, my question is can I file two tax returns for two years, one for 2018 and one for 2017 since I already filed one for 2018? Or do I file an amendment, or I can only wait till next year?