first try an easy fix, take a syringe or oil can, take off the clutch cover.
squirt some marvel mystery oil into the central hub. run bike spin off excess, tap center button with small hammer lightly with the clutch lever engaged. it will free it up if its stuck. otherwise you need to re adjust the lever knarp. so there is some slack in there. it should free up and the marvel will not glaze the pads but will burn off after a dozen miles.
after that, it is dissassembly, clean all parts in brake cleaner after lightly sanding the central hub towers and disk.