I had a cockatiel once and was mean from day one bit to make you bleed and would go out of the way to do it. I had him for 10 yrs he never changed. It was when I got a second cockatiel that I learned birds can be sweet. She was loving and affectionate and so we're the 2 budgies and my conure now. Maybe some birds are just butt holes. 😁 But as mean as he was I learned to love him very much and would not have traded him. He learned to love me too cause he bit me the least.

Take your time and give the bird its space. Keep an even quiet tone and feed a treat often (same thing). Watch step up training, Touch stick/clicker training with a daily time schedule. Try to keep these events away from the other birds, for a time. jh