They can be a handful to train since they are very smart & thrive on emotion.
You almost have to react the opposite way & never threaten them.
They are basically as smart as a 3yr old kid & will remember everything.
You have to gradually approach them from a distance, slowly getting closer over a few weeks. Start at the doorway & slowly get closer without getting them mad. After you get very close, they may lunge at you, trying to be intimidating.... you have to not flinch & talk calmly to them. Gradually you should be able to get them used to your distance. Stay close but beyond reach of the beak, as they can snap a wooden spoon. Many times they are not as mean as they act, but just trying to prove their dominance. Once you show, you are not scared, they will likely stop trying as hard. Then you can work on gaining their trust. It takes a while with a mean one, but most will come around.
Mine is now between me & the laptop, with her beak pressed against my cheek while getting petted. They are amazing once they take to you.