The clip goes toward the sides of the car.

Where it pivots, move the seat toward the center of the car and then you will be able to see a little bar that you can put the clip on.

You will know that it isn't secured if you push the seat toward the wall and pull up and it comes off. If you need to remove the trunk carpeting, just pop all the rivets off and pull the plastic that holds onto the top of the seats out.