How do you fix the clutch spring on a 1996 Geo Metro?
If you are referring to the little springs inside the clutch
assembly itself, you don't fix them, you replace the clutch.
If you mean anything else in there with the clutch, see the above anyway, that'll get you inside.
No, a 91 metro transmission will not fit in a 98. A 91 will fit any metro between 1988 - 1996 though. After 1996 a lot of Metro's became 4 Cylinder which made them different from the previous generation metros. It may fit if the engine sizes are correct (1.0 litre 3 cylinder to the same but do not mix and match).