what to do if outdated baking soda was used in cookie dough?

Test the baking soda by adding a teaspoon to a cup of water. If it fizzles, it's still good. If nothing happens, pour the contents down the drain.

Baking SODA doesn't go bad (expiration dates aren't regulated so often they are less meaningful than we'd like). Baking POWDER does. Baking soda is just calcium carbonate. It should be fine as long as it was baking soda you needed.

did you bake the cookies yet? They will have less of a rise, but will still be edible. If you need "perfect" cookies for serving and you don't like the way they turned out, or don't like the flavor, you'll have to start over but otherwise, they should be ok.