Hi!
Do you mean to make the sun in the sky less bright? Or, is it how the sun washes someone or something out with too much light? There are many tools or techniques we can share, but it all depends on what you want to accomplish.
It would be helpful if you could provide a screenshot of the image you want help with.
Also, what platform are you on, Mac or Windows? And what version of Photoshop are you using?
Michelle