You can! As long as your steaks aren't frozen on top of each other—they have to be frozen in a single layer or separately. Pull them out of the freezer and add them to the water bath when it reaches temperature. Be aware that adding frozen meat to your sous vide bath will make the water temperature drop, so you're going to have to wait for it to come back to temperature. Once there, start timing, with the addition of an extra hour because of the freezing.