If it's part#30 in the drawing,,the floor plate spring retainer clip,,,
They are just that, a spring clip.
Slightly arched and they snap into and out of place with a bit of effort.
I usually use a small dia wooden dowel to tap them in and out of position if finger pressure alone doesn't do it.
Their arched shape and the fact that they are a spring and snap into position is what holds them in place.