If you cannot download the program then you will either need to go old school and get the paper forms from the feds & state and complete if manually  OR  find another tax program or paid preparer.

To file an amended tax return that was completed and filed using the TurboTax online editions, you must amend the tax return on a desktop computer, either Windows or Mac based.

If you have a Mac computer then go to this TurboTax support FAQ and request a 2016 Mac download so you can amend the tax return - https://ttlc.intuit.com/questions/3449967-amend-prior-year-return-mac-software-request

You will need to download the tax data file from the 2016 online account.

When you sign onto to your online account using the exact same user ID you used to create, complete and file the 2016 tax return you will land on the Welcome Home screen.  Click on My TurboTax at the top left of the program screen.  This will take you to the 2016 Timeline.  Under the section Some things you can do:  Click on Download .tax file

Or if you land on the Welcome Back screen click on the blue link Download your .tax file

An amended tax return has to be printed and mailed, it cannot be e-filed.