There is an adjustment screw on the supply line for the pilot. It's possible that it may have to be opened a little more to get propane to flow to the pilot. I would try turning the screw about 1/4 turn and try to light the pilot. If it lights, adjust the flame on the pilot before trying to light the oven. Since you haven't used the oven but once in three years, there may be a little debris of corrosion in the line at the adjusting screw. If you are not comfortable in trying that, then see a dealer or go to your local propane supplier and they can probably help you.
John