Day 20 and humidity dropped

[Bodle]

I am hatching chicks in my classroom. It is day 20 the humidity has dropped suddenly to 45. There were several eggs that has started pipping, but has not progressed much. How do I increase the humidity quickly?

 

[Knobby]

I just did a batch using the dry hatch method. At lockdown my humidity ran around 25-40%, but once the chicks began to pip and hatch, the humidity shot up to 60-80%.