I want to re-start a return, clearing all previous entered data, how do I do this?

Start a new return. Once you've got a new return on the go, you'll be able to delete the one you created first.

Here's how to start a new return: https://turbotax.community.intuit.ca/replies/3288128

And here's how you delete a return: https://turbotax.community.intuit.ca/replies/2647999