Typically these would be soldered to the cable using standard methods. Though its possible some are now crimped...no id9ea correct shape/size of crimp needed.
EDIT: Oh. perhaps thesevare end ferrules, not cable nipples? Those are i believe slipped on the plastic cable casing by force fit, sometimes with some heat on the plastic.
Ive seen yourube videos by Lunmad showing how he removes/refits these by this method.
Not sure any crimping needed but even just a slight denting with crimp pliers should work ok.