Two techniques. The first one is pretty straightforward. What I show is actually a variant where you grab the dagger to apply the lock.
The second technique is a little unclear, because if the attack is from above as the text suggests, the arms can't end up in the position depicted. Push the attack down, grab around his neck, throw him backwards.
One way I think the position depicted can be reached, is when the attack is to the fourth opening. This then looks very similar to one of Marozzo's dagger defences. (Note relative arm positions)