It takes a while to tame a bird. Took me around a month for my first female cockatiel. Now working on my second male cockatiel. Best thing to do is at first to start letting him go onto your hand and start to trust you. When you get bit, don’t react because it allows them to know that you are vulnerable. Slowly start to have them with you a lot. Buy a perch stand where you can leave near you. I can link one I purchased. https://www.amazon.com/dp/B089F3MV8B/ref=cm_sw_r_cp_api_i_03A2KDD32TY8R4DQN9ZE?_encoding=UTF8&psc=1 allow them to sit on this while it’s on a desk. And maybe just play some video games or use your computer so they know you aren’t a threat. With feeding wise, try parakeet/finch seeds. Sound weird but the second cockatiel didn’t eat anything except that at first. And now I’m on my way from transitioning from a seed diet to a pellet diet. Also feed it fruits and veggies. Look online as to what you can give him. Eventually he will eat and not starve himself. Just make sure the food bowl and water is very accessible.