If you found a live shell – if small just put in a plastic container. Then poor boiling water on it. Don’t boil any shells under the heat as they will crack.
Any shinning shell Cypraea, Oliva, Strombus put them in a sealed plastic container and leave it in the sun. The animal will fall into sleep and die after a short time maybe two hours for thick shells. I do that with large shells and the animals come out easily without leaving organic bit inside.
Freezing can work – mind that cracking or blisters can occur on the shells surfaces.