cockatoos like my quakers are re homes for screaming in huge numbers. Tho toos beat my quakers hands down.
I do think you can make progress and see reduction in screaming. But what you are left with may still be more than you and neighbors can tolerate.
It's takes much like what's already been mentioned, a whole bird and environment make over. That's where I start with screamers before direct behavior modification. A great and healthy diet, a great cage, lots of perch size, filled with different hardness chew stuff and a mix of toys in the noise maker, foot toys, manipulation toys, foraging toys. Several out of cage hang out spots. And a health exam by veterinarian.
Then for me its all about preventing screaming sessions from getting started as much as possible, knowing triggers. I've found ignoring screaming does nothing to stop it. So I interrupt, and redirect as soon as it starts. Lots and lots of praise when quiet . And I've had to build off quit times of mere miniuts and create habits of quiet.
There can be some success with pairing with soothing music. You start out by playing soft soothing music in the evening as tgey go to sleep, and when they nap. After that pattern is established, you can play the music to induce calm at other times with some success.
Someplace I've really given detailed screaming help advice. Maybe I can find that post and link.