Cushing's can be helped with acupuncture but it is a difficult condition to treat. I highly recommend you consult with an acupuncturist in your area and begin treatment.
As you are asking about acupressure, there is little that can be done (in my opinion) for conditions of this nature with acupressure. I just don't feel the effects are strong enough. Acupuncture studies have shown mixed effects on cortisol levels with some showing increases and others showing decreases - possibly (but not conclusively) showing a regulatory effect. In general we know that acupuncture reduces stress hormones and levels but all of the mechanisms have yet to be determined. One study which used a point combination called the four gates (LI 4 and LV 3, bilaterally) showed decreased cortisol responses to an external stressor. Of those I would suspect that LV 3 would be of primary importance from an acupressure perspective.
You could try points strongly calming acupressure points such as PC 6, HT 7, LV 3 perhaps with LI 4, but I would recommend you consult with a professional locally and obtain full acupuncture treatment. From that the practitioner should be able to make more precise recommendations for you.