Have you figured out was his current favorite treat is?
Ask him to step up and show him the treat. Hold the treat far enough away that he can't get it without stepping up. When he steps up give him the treat but not until he does. Reserve those treats for training only.
I'm happy to hear you two are making progress. Take your time and try your hardest not to lose your temper with him. I know you reacted in reflex. If you see that he's posturing and acting aggressive don't try to approach him until both of you are calm. Birds, like people, have their moods.