If you amended the 2017 tax return using the TurboTax online editions, you were requested to save the original tax return as a PDF before amending the return.  If you did not save the original tax return, the only tax return available from the 2017 online account is the amended tax return.

You can also get free transcripts of your federal return from the IRS - http://www.irs.gov/Individuals/Get-Transcript

For a fee of $50 you can get a complete federal tax return from the IRS by completing Form 4506 - http://www.irs.gov/pub/irs-pdf/f4506.pdf