Before you started your return, you should have entered the code at turbotax.ca/activate (or https://shop.app.intuit.ca/activate?rootProfile=ca&locale=en-ca). Since you have already started a return, you can put the activation code in the coupon code box when you pay for your return. You can get to the payment page by opening your return and selecting Finish & File from the bottom of the left side menu.