Here is something you can do for a bird that is screeming.
When your bird is screeming and you go to the bird at that time, you are telling the bird it's ol to screem.
Prase the bird when it's NOT screeming.
Drop a pan, or get a lazer light and flash around the floor (NOT AT THE BIRD), this will distract them, then you go and tell the bird how good they are doing. In time it might just stop or slow down the sccreeming.
NOTE: This will not work on all birds, some might want to screem all the time.
Remember: If you do not pay any attention to your bird, they have to get attention some how, so they will screem out, or bite. Negitive attention, but they are getting it.