Welcomed to the forum. Congratulations on your new cockatiel.
It is frustrating, when new birds are fearful. It does take time, and a week isn't that long for him.
What's your birds name?
Having a large cage, placed were he can see stuff and be part of everything, but the back of the cage against a wall, helps. Plenty of perches if different sizes. And place perches on the sides and top of the outside of the cage. Do you can open the door and he can climb out and have a place to hang out.
Keep talking , singing, whistle to him. Put a chair next to the cage and spend an hour reading out loud to him, your texts, a book..
Offer lots of different veggie, and leafy stuff, maybe done apple, or fresh corn on the cob. I offer veggies in a large wide dish on the bottom of the cage, they do better if they see everything spread out.
Always talk to him and tell him what you are doing. Like say hello " name" everytime you come to the cage,tell him when you are change ezte or food or cleanings. He will like the predictability, of knowing what's going on. Always great him when you get up, always tell him when you are leaving.
Set up a small treat dish, and put the tiny amount of millit spray in it, then sit buy him and talk. He will soon associate you with good treats, eventually he will take them by hand. You can try popcorn, safflower seeds, or sunflower seeds as a treat, put one in the treat dish everytime you come to say hi.
Others will give you good advice. You will get there.
