I will assume you still have your 2017 TurboTax program. When you click on the "State" tab, it will tell you to click continue to work on your state return. The next page shows the free state you chose with the purchase of the program (in your case, Oregon); below that it will tell you to click "Get Another State" if you need to do another (in you case, California). When I clicked the button, it opens a page saying it will take my to a secure online site to "finish my order". I would assume it will walk you through the steps to buy and download your 2nd state.
