If you need to correct your Social Insurance Number (SIN), select “[YOUR NAME] Personal Information” from the “Setting Up” tab. Change the SIN number and click the “Continue” button to save your information.
If you can’t see a “Setting Up” tab, use the grey “Back” button to go backwards through the pages until you get to the “Now, let's get [YOUR NAME] information” page.
If you are just starting your return and the program is asking you for a SIN, you can find it on your T-Slips, pay slips, and any mail you have from the CRA (like last year’s notice of assment).
If you have TurboTax Live Assist & Review, here is how to talk to a Tax Expert: https://turbotax.community.intuit.ca/replies/3456106