I have not found a way to add this to the several excellent threads regarding how to replace KIF Elastor type clips so will start this as a new thread.
The most valuable piece of information from the old threads is the recommendation to use clingfilm to cover the work area!
The other crucial information is that the way to release the clip from its hinge is simply to pull on its cross bar. My contribution is to add that this implies that to replace the clip it can be pushed back into the hinge if the long legs have both been cliped in place.
Therefore in replacing a KIF 3-3 (in a Longines Calibre 342) the clip (with the top jewel in place) is laid loosly over the jewel and then covered with clingfilm. The two long legs of the clip are then pushed into their seats using a fine tiip oiler. The cross bar of the hinge end of the clip can then be simply pushed on so that the hinge end of the clip goes back into place.