Tankueray
Bird Nerd
If that's a standard forced air styrofoam incubator, you should be able to add water without opening it via holes in the bottom or at the top with a turkey baster or syringe with a tube attached to it. Open up your vent holes so there's plenty of oxygen in there and watch that humidity level.
Edit: It doesn't look like styrofoam. Use whatever that incubator's functions/features have to try to accomplish the same thing though.
Edit: It doesn't look like styrofoam. Use whatever that incubator's functions/features have to try to accomplish the same thing though.