Entering OR Federal Pension prior to Oct. 1991

Hello,

My husband is a retired AF officer.  According to Oregon tax law he can deduct the amount of service prior to Oct. 1991.  I can't figure out how to add this to turbo tax.  He served 100/328 months or 30.5% before Oct. 1991.  This part of his retirement isn't taxable in OR. I tried hitting the edit button in the OR Federal Pension Summary, but nothing happens. 

Please let me know how to enter this since last year I had to do the OR taxes by hand to not pay 30.5% of his pension.

Thanks,