Are you trying to view a 2018 return? You can look down at the bottom of My Returns>View All Returns for the PDF of past returns if they were filed using NETFILE and you used a paid version of TurboTax. Or you can login to TurboTax 2018 here: https://ww1.2018.turbotaxonline.intuit.ca/
If you are still not able to find the return, this FAQ lists a few reasons you might not be able to find the TurboTax Online return you’re looking for: https://turbotax.community.intuit.ca/community/importing-transfering/help/why-can-t-i-find-my-turbotax-online-return/00/873627