No further details provided
Usually, to the right...in my experience. You can confirm your setup by putting a flashlight in the fireplace or by lighting a fire. You should very easily see the light from either as the damper opens. The Fireplace Screen Damper is your brake peddle.
So, only open the damper enough for the fire to maintain itself with a moderate flame. You'll get a good and complete long-burn and not a "roaring" fire that goes through wood or synthetic logs very quickly and inefficiently.