The IRS does not amend your tax return. Only you can amend a tax return that you filed with the IRS by using Form 1040-X.
To access your current or prior year online tax returns sign onto the TurboTax website with the User ID you used to create the account - https://myturbotax.intuit.com/
Scroll down to the bottom of the screen and on the section Your tax returns & documents click on Show. Click on the Year and Click on Download/print return (PDF)
If you used the desktop CD/Download editions installed on your computer, the only copy of your tax data file and any PDF's will be on the computer where the return was created. TurboTax does not store online any returns completed using the desktop editions.
Or go to this IRS website for free federal tax return transcripts - https://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
If the IRS changed something on your 2018 return and--for example--reduced your refund---TurboTax will not know about it. After you file your tax return, TurboTax does not get any information from the IRS or state. So....we are not sure what you mean when you say the IRS "amended" your return. The tax return on record in your TurboTax account or hard drive will be the one you personally prepared. It will not reflect any changes that the IRS made.