You would just have to be patient with him sit next to him read him a book and slowly he'll start to trust you my cockatiel kiwi took me about 2 months to get her out of the cage and even now she still gets nervous when I make big movements. You could offer her treats form OUTSIDE his cage and don't make large, sudden movements around him let the bid set the pace don't ever rush him it'll just make him even more scared. Most important thing is to be patient and never give up, it might take a long time but when a bird is bounded to you it is the absolute best feeling in the world, trust me its worth it.