OR resident filing 1040 standard deduction. Not able to get IRS credit for long-term care premiums but can under State. Where is this on the OR state form guidance?

In the OR state interview you will be asked to enter the amount of medical expenses entered that can be allocated to the qualifying taxpayer (age 66 or older) for the OR special medical subtraction.

If you're using TurboTax Desktop, you can make the entry directly on Schedule OR-ASC, Section B, Code 351, which will show on Form 40, Line 13. 

In Interview mode, under Here's Income that Oregon Handles Differently, choose Other Subtractions and Continue.  On the next page, check the box Subtraction you haven't already entered, and on the next screen, scroll down the Other Subtractions form to 351, and enter your LTC premiums amount.