If you were a nonresident alien for tax years 2017 and 2018 you need to file a Form 1040NR. TurboTax does not support Form 1040NR.
See this TurobTax support FAQ for information - https://ttlc.intuit.com/community/forms/help/does-turbotax-handle-form-1040nr-for-nonresident-aliens...
