ok, i've done it both ways when that's happened. i've opened it up to let moisture out, and i've left it alone. same results either way. supposedly, if it's that humid, a chick has a chance to drown. i havent had that happen. if you open your bator, you're pulling moisture out of the eggs as well. i do open my hatcher, but that is because i constantly have eggs going in and out. and when i open it, i always add more hot water to it.
my advice would be to leave it alone. the worst that will happen is your chicks wont dry, and you can pull them and put them under the light in dry bedding and they'll dry within an hour.
if, after you do it this way, you dont like the results, then next time, open it up.
also... if you're using a digital, it very well may be more humid in there then it's reading. sounds stupid, but i finally went and got a non digital off of
ebay from someone in england because i was sick of having to replace digitals when they went haywire. it's in celsius, but very very accurate, and very easy to read (it's a big 4 inch circle, temp on top, humidity on bottom)
remember, mother nature isnt perfect, and i have yet to see a fan or a humidity gauge on a chickens ass.