Raise the humidity to 75% or higher.
Place a clear Ziploc over the top to keep them humid if you can't get the tent humidity up.
Use a syringe/q-tip/straw to keep those seed hulls moist. They should have cracked before they popped out of the soil but now you have to do the soils's job of wetting the seed hull.
I've saved one before like this by going in and soaking the seed hull in a spoon of water, or a syringe with water, just for a minutes whenever I have a chance to throughout the day.
Start now, get them moist!