If your room humidity is about 57 now, you are unlikely to need a de-humidifier. Can you alter the ventilation? Increasing the ventilation will also cause your eggs to dry out more and thereby avoids the necessity of dehumidifier. My first time hatching in the middle of summer, I used dehumidifier, but the heat output from the portable unit caused the temps to rise in my LG.
You should do well to dry incubate with a room RH of 57.
you can also add plain dry rice to a bator to reduce humidity.. they also sell those little packets of silica gel which can be safely put down in the bottom of a bator.. though I prefer the rice method if it's really needed..
usually you don't need to decrease humidity if you are incubating dry..
if only a few eggs are losing weight too slowly and you have a bator with a fan .. it's usually just a matter of moving those eggs closer to the fan which will aid in drying them out a bit more