They job of a hygienist is usually to manage your gum health, they will often clean your teeth using ultrasonic scalers and hand scaler and will also polish your teeth.
What does a hygienist do?
Can they make my teeth whiter?
They can usually remove topical staining, staining that is intrinsic will need to be removed with whitening.
What if I have stubborn staining?
Usually they can air polish teeth to remove stubborn staining especially staining that is picked up on your white fillings, but everything has a limitation.