need replacing.
it is difficult to answer your questions without some much more specific information. some photos would help.
there is normally a threaded fitting embedded in the plaster and then something screwed into that. if so, all you need to do is unscrew what is left of the part that used to be screwed in. if something more complex than that is going on, i can't imagine what it is without more information.
my pool is about 10+ years old and the eyeball fitting seems to be drying/cracking in small parts but not completely coming apart. as a result, only the eyeball portion itself is easily removable by hand but the actual 