You can try taking egg from fridge, cutting hole and emptying it. Then take acizzors and cut a big round shield shape from side. Wash and dry that carefully. Carefully pick broken shell away. Put glue around the edges of shell piece and then rest it on top and lightly tap down.
You should be able to do this without removing it from the incubator. Don't worry about the temperature or humidity. You should have the top off in less than 20 min.
There is still the chance of bacterial growth but that's your best bet.
Okay, is the membrane surrounding the chick still intact? Or is that broken, too? If so, is it bleeding? Or did you notice any blood? It might, might be savable if that membrane is still there, and no bacteria gets in it.