The only way to do this is to use two pairs of pliers (or very long BBQ tongs), attach these to the hedgehog’s spines either side of the animal and pull hard. It does seem cruel but the hedgehog will die if it is not rescued from the drain.
Please make sure all drains and holes are covered to protect hedgehogs, other wildlife and pets.
Once you have extracted the animal put it in a secure container or DEEP box and take it to a rescue or vet immediately to be checked over. They can be suffering from hypothermia, ingestion of water or chemicals poured down the drain and will need treatment. Do not just release them.