When using TurboTax Free, click on the heading titled Provincial and click on Get Started.  Click on Continue until you get to the screen that says, "You may qualify for the 2018 Ontario Trillium Benefit".  Answer Yes to the question, "Did any of these apply to you and you want to apply for the 2018 OEPTC?" and click on Continue.  You will then be prompted to enter the details of your rent paid.