I assume you want to solder the wire onto the plug.
The outer cover just unscrews
To remove inner cover:-
There are two plastic clips on each plug which have to be pushed in whilst withdrawing cover. It's easy to break these clips. so don't push too hard or force anything. The clip has a "fish hook" like end which acts like a ratchet. The plug will hold together if you only break one clip.
When you solder the wire use a low powered soldering iron and try not to melt the plastic.
BTW, I think they are very good, but I use a DNM pre-amp where plastic is king.