If you're looking to download your past tax returns, and have filed with TurboTax last year (or in years past), you can access your past tax return information in Tax Home.
See instructions here: https://ttlc.intuit.com/questions/3404575-how-do-i-access-my-prior-year-2017-return?jump_to=answer_5...
If this didn't answer your question, can you be more specific with what you cannot download?
