It doesn't happen often, but if your pet parrot becomes muddy or covered with sticky food, it will clean itself by preening and bathing as normal. If the stains look stubborn, or if they are in hard-to-teach places, you can help out by spraying water on the bird with a mist sprayer.
This only applies to no-toxic dirt, though. If the contaminants are oils or paints (sometimes a hazard if the bird is allowed to fly free in a room), he problem is much more serious. A hand-tamed bird can be gently washed with warm water and a bird-friendly soap.
Birds as tame as these Hahn’s macaws are easier to clean
If washing the bird, avoid getting the soap in its eyes. The parrot will ingest some of the soap during the cleaning process, which is why it's so important to use something non-toxic. If your parrot is not hand-tamed, or if the stain is very hard to remove (tar, or oil-based paints, for example), you will need help from a vet, who can sedate the parrot before giving it a thorough clean.
A newly-cleaned parrot will often shiver for a few minutes afterwards - this is the bird's way of sorting out tousled feathers and generating heat to aid the drying process. Never use a hair-dryer to speed things up, though, and don’t towel-dry the bird, as this may damage the feathers.