Act like ur carrying ur hands or my trainer says act like ur fingers r at ur elbows. Another thing I do is if the horse is getting frustrated with my hands I open my fingers and hold on to the reins with my index finger middle finger and thump
Put a crop side ways in your hands as you ride . And think about pushing a car or something flowing with the horses step and stride and staying relaxed as possible.
When I'm trying to soften my hands and elbows I try and relax my whole body and move with the horse. You can also think of your elbows as a door hinge that opens and closes slightly with the movement of the horse.