Dough dry on top

Mist the dry part lightly with water and let it sit for a moment or two to soften. If it's very hard, pick it off, just as PoLC suggests. Best to cover the dough with plastic wrap, or rise it in a container with a lid (you don't need to seal the container, as the gas from the rising bread might pop the lid off anyway. Just place it on the container.)

If its just a thin dry layer, it shouldn't be a problem, i'd just shape the dry layer to the inside. If its thick and crusty you could try to pick some of it off. There should be no reason to start over though.