I have done some research and found an answer for you. I hope this helps provide some clarity for you. Follow the links provided in the answer and select "2014" and you should be guided to a step-by-step answer to amend your 2014 Oregon state tax return.
Once your return is accepted, you will need to amend your state return. Amendment software through TurboTax should be available in mid-February. To amend just the state, first, fill out an amended federal income tax return, Form 1040X. Then, get the proper form from your state and use the information from Form 1040X to help you fill it out. Like the IRS, your state uses a special form for an amended return. Many states also use the X suffix for the form number.
Please see this TurboTax article for more information on amending: https://turbotax.intuit.com/tax-tools/tax-tips/IRS-Tax-Return/Amending-Your-Income-Tax-Return/INF120...
How to amend for the 2014 Tax Year will be posted here when the amendment forms have been finalized: https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed