Clams do not die when frozen unless the clams are frozen longer than 3 months.
When frozen clams can stay alive frozen for up to 3 months and after 3 months in the freezer the clams can then die.
So make sure to use the frozen clams within 3 months so that the clams do not die.
If the clams have died before you cook them then throw them out because they can contain bacteria that can make you sick if you eat them.
When thawing out frozen clams place the frozen clams in the refrigerator overnight and then the frozen clams will be thawed out and ready to cook.
You can then steam cook the clams or boil the clams to cook them.
But make sure the clams are alive when you're going to cook them.