Sorry---you cannot use the desktop download on an iPad. You can only use it on a full PC or Mac. If you do not have access to a PC or Mac, you will need to seek a refund for the download and then use online TurboTax software instead. You cannot pay for online TurboTax using that code.
To request a refund from TT ; https://support.turbotax.intuit.com/forms/refund-request.jsp