Simple just buy the multi finger gripper type, I have great luck with this one. simply open till you can slip it over the crystal
and crank down till the crystal loosens up down over do it, if it starts to turn easily then it should just pull right off. reverse to install but you will need the setting plate. the pics show what you need. Doesn't work with every crystal but just about.
These have worked well for me although there are the occasional
crystals that can be easily pushed back on with thumbs.