The answer to your question is that, after finishing your federal tax return in TurboTax, and then proceeding into the Oregon state module of the program, you will encounter a page titled "Take a Look at Oregon Credits and Taxes" or similar (depending on your particular version of TurboTax), which is a is part of the standard Oregon taxpayer interview.
Then, you will select the Start or Update button next to the "Uncommon Oregon Credits" line. This will take you down the pathway that you will need to complete, in order for the TurboTax program to generate the proper tax credit and state credit code on your Oregon tax return.
Please refer to the several screen-capture images attached to the bottom of this text answer for a visual guide; simply click the pictures to open.
Note that if you've already gone through the Oregon TurboTax interview once (or more), then to find the beginning screen for the Oregon Cultural Trust data entry you will just begin the interview one more time . . . and then answer the necessary questions according to the screen-capture illustrations.
Thank you for asking this question.