License codes (16 digits) cannot be entered on the TurboTax mobile app or in the online version, as they are specifically for the TurboTax Desktop software on Windows or Mac. If you bought a CD/download, you must install the software on a computer to use the code.
Go to this TurboTax website to download the edition you purchased to install on a personal computer - https://turbotax.intuit.com/personal-taxes/cd-download/install-turbotax/