The only way to give your accountant access to the past returns in your TurboTax Online account is to give him or her your user ID or password. Then the accountant would have access to everything in your account, and could do anything that you could do. That's not a good idea. It would be better to download PDFs of your past returns to your own computer, then give the accountant copies of the PDFs. (You should always save a PDF of your tax return on your own computer anyway.) The following FAQ tells you how to download a PDF of a past tax return.
How do I access a prior-year return?