Yep, do a search and you'll find lots of info.
But I'll also tell you what I do (which is different from what everyone else does.
Everyone has their own way, and you just have to figure out what works best for
you).
I use Tide with bleach
alternative. To wash a crest, I wrap the bird up in a towel, kinda like a burrito...keeps the bird together in one nice neat package, so you can hold them securely while leaving one hand free for washing. I hold the bird on its back--so its head is upside down almost--just like when you go to the hair salon & you lean back over the sink to get your hair washed. I hold the bird football-style with my left arm, using my left hand to cradle the neck, allowing the bird's head to tip back a bit. This way I can wet & wash, but I can see the bird's eyes & nostrils and avoid getting water & soap in them. I wet the crest, add a small bit of Tide (a little goes a long way!), and work in very well. If there are particularly funky feathers, I might use a soft toothbrush on individual feathers, working in the same direction as the feather, to work out any icky stuff. Let the Tide sit on the crest feathers for several minutes! Then rinse, rinse, rinse. Repeat if you need to. Keep in mind that the birds' crest will look more bright & white when it is completely dry than when it is wringing wet. So don't get too discouraged if the crest seems to have a yellow tint even though you've washed it a couple of times. It will brighten up when it dries. You may find that you don't get it
completely white. Some staining from the environment, yellowing from the sun, etc., just won't come out in the wash. But you can do amazing things with a good bath!
Other things folks use to whiten up the crest are dog or horse whitening shampoos, Cowboy Magic spot remover spray for horses, clothing stain remover sprays, or a couple drops of old-fashioned laundry bluing in the rinse water. I've used these things (except for the bluing), with varying degrees of success. I like the Tide best, personally. But lots of folks swear by other products so, again, use what works best for you!
Good luck!!