If you used TurboTax Online, sign in to TurboTax Online for the tax year 2018 here: https://ww1.2018.turbotaxonline.intuit.ca/.  If you used TurboTax CD/Download and you saved it on your computer you can simply go to the Start button on the bottom left of your screen and click on Start and you will see a small search bar - type in .tt18 and you will find it there.  If you did not save it, unfortunately, there is not a way to access it.