I don't know... I never "taught" my boy, but he blows me kisses all the time when he is in a good mood. I guess he just learned to connect kisses with something good or positive (I blow him kisses too when he is a good boy).
I made kissy noises, working to slowly toward Joey's face, until I kissed his beak. It took quite a few attempts over a few weeks. He shied away a bit at first, but now loves having his beak and the top of his head kissed. If I am kissing the top of his head and stop befoe he is ready, he will headbutt my lips til I start again.
My boy doesn't really "touch" me when he kisses me, he just blows me kisses (makes kiss-like noises) from a short distance (for example from my shoulder). I can even predict when it's going to happen because his crest goes flat apart from the tip and he opens his eyes really wide - then he blows me kisses.