Since your cockatiel is reacting so strongly to your opening the cage, just sit by the cage doing nothing but being there. Read, watch TV, whatever, but give the bird some time to become accustomed to your presence. After a few days of that, try quietly speaking to the bird, or offer it some fruit or millet through the bars. Do that for a few days, then open the cage daily for a few days, then a few days of just putting your hand in the cage without approaching the bird...you see how this is going. Take it in very small steps and let the bird become accustomed to each step before moving to the next. By the ay, this advice is offered by a guy who has had budgies, conures, cockatiels, cockatoos and an African Grey. The African Grey stalks me anywhere in the house, and attacks me. I figure I'll need about 100 years of gradual acclimation before she will like me (she loves my wife, and they are one-person birds). Good luck.