I cannot tell specific because I don't know a lot about cabbage. But he is talking about insecticides containing BT-Toxins from bacteria "Bacillus thuringiensins" Wikipedia Link. Of course I do not know which forumlas would be available to you. But in all cases it is important to use it at a time where you can reach the worms while they are still small enough for the toxins to have an effect. Correct timing is key. The other suggestion was about covering the young cabbage heads with cloth or a fine net. That way the moths cannot lie their eggs in them. For that you'd have to know when the eggs are laid and when to remove the cloth. CC: @johntimaeus@infosec.exchange