Looks like after you connect the wires, those 'wing' springs should fold back against the body. Then, holding the springs against the light's body, insert the assembly into the panel opening until the springs are inside the opening. Then you can release the springs, push the assy. flush and they will spring back over the inside of the panel holding the light and bezel in the opening. On some lights, the body is installed this way and then the bezel is rotated on the body to secure. Can't really tell from the pics.
Edit: Must be getting late, after re-reading, the springs are probably mounted to the body by inserting into slots, screwed or welded. If tack welded, you might have to get a new assembly with them already installed. Sorry, that's all I have for you.
Jan and Bob