There's no one-click clear or start-over button, unfortunately. With a return you've already paid for, the best thing to do is use the Find feature to navigate back to the spots in your return you'd like to modify. Some things though, like your SIN number or if you chose to prepare your return together with a spouse, are not editable.
Here's how the Find feature works: https://turbotax.community.intuit.ca/replies/3484165
Alternatively, you could choose to start a new return from scratch. If you do that, give us a call and our phone team will refund the cost of the return you paid for but didn't file.
Here's how to start a new return: https://turbotax.community.intuit.ca/replies/3288128
And here's how to reach us by phone: https://turbotax.community.intuit.ca/replies/3288128
If you would like to contact our phone support team, you can call them at 1-888-829-8608.