It's just a tooltip? So no way to know whether you've done it properly.
I'll tell you that you'll need to make a trigger for it, and you won't be able to simply use bash either.
You'll need a damage detection system & roll a dice. If dice = 14 or less out of 0 to 99 then spawn a dummy unit that casts warstomp.
You could technically do without a DDS and simply use "a unit is attacked", but then the player could spam click attack & stop to make the trigger fire without attacking for real.
p.s. If you're using the latest version of world editor, then maybe that new event has been added which fire when a unit finishes their attack animation, and so you wouldn't need a DDS if that exist either. (But idk since I don't use newer version of world editor myself.)