You are not able to directly upload into the TurboTax app, however, you can sign into TurboTax Online and upload your tax return and then continue in the app as everything is synced between TurboTax Online and the mobile app.
For instructions on how to transfer your returns into TurboTax Online, please see this helpful FAQ: https://ttlc.intuit.com/community/entering-importing/help/how-do-i-transfer-last-year-s-return-into-turbotax-online/00/25953
For more information on how to use the TurboTax mobile app, please see this FAQ: https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-use-the-mobile-app/00/26828