Using the online version you can  log back in and you will still have the same page you last worked on. If you want to start  a new return you

https://ww1.2015.turbotaxonline.intuit.ca/

Click the Tools icon and then click Return Manager. You should see the returns you created (filed or not, the returns will still be there).

If your using the download version you would to do the following:

Click on the Icon and once open you would go to the top left and click on open where the return would show up with the name of the person you are doing the return for or for yourself.