The only way to open a tax return that's on your computer (a .tax20yy file) is with the CD/Download TurboTax software for the corresponding year. You cannot open it in the TurboTax Mobile App or with TurboTax Online.
If you no longer have the software, and you only need copies of the returns, you could try TaxPrinter. You send them your .tax file and they send you back a PDF of the tax return, which you can then print with Acrobat Reader. TaxPrinter has no connection with TurboTax. I have never used TaxPrinter, so I cannot make a recommendation. I'm just making you aware of it.
It's not clear what you mean by "the Turbo Tax app." Are you referring to the TurboTax Mobile App that you use on a phone or tablet, or to TurboTax Online, or to the CD/Download TurboTax software that you install on your Windows or Mac computer?
