To enter a new licence code in TurboTax CD/Download 2019, select Help > Purchase More Returns from the top menu. Then click on the "Unlock Your Purchased Returns Now" button. A pop-up window will appear where you can enter your new code.
Please note that the CRA limits all NETFILE certified tax software to a maximum of 20 returns. If you have already NETFILEd 20 returns you will have to print and mail any additional ones.
