You would request refunds by filing an amended return for each year in which your original return was incorrect.
You'll find Oregon's law on requests for refunds here: https://www.oregonlaws.org/ors/305.270
Note that if you deducted your state income taxes on your federal return for any of those years, you may also have to file amended federal returns.
You may want to consult a local tax professional for help with your situation.