You add a dish of water or something soaked in water.... the dish is easier to regulate. The larger the surface area... the higher the humidity. I use a small bowl... if I fill it high where it is wider, I get a slightly higher humidity... if it gets low.. it drops by about 15 degrees or so.
Do you have an incubator??? They need to be in a controlled environment.... a cooler, a wooden box, etc... but they also need to have vents so that oxygen can get in.. they are living and breathing..... even the egg.
There are still air and forced air incubators. You just have to adjust the temps accordingly. Search the forum for more posts on this. Everything you need to know is there somewhere.