first of all i am asking this question for a friend.i get the council to sort mine out.
ok i have told her to use WD40 to loosen the tap to turn the water off but still too tight.i think its a cold tap which needs fixing.the bath tap
You might have to turn the water off and remove the valve to clean it out and free it up.
Take off the handwheel, then the shroud, then unscrew the valve to remove it.