I've had both (passenger side and drivers side) cup holders out several times. Seems like someone hits one of them with a knee and knocks it out of place. They are easy to remove and replace.

The cup holder pivots on plastic pins that fit into holes on each side near the bottom. You can carefully grab the cup holder and twist one side's pin out of the hole. It's tough to describe in words....just pull it firmly to one side and then twist the other side free. You may find a thin screwdriver helps to unlock the pin.

Pay close attention to the orientation of the ultra thin spring that comes out with the cup holder. It will only work if you get it back in exactly right. Every hook and curve of the spring has a purpose and you should be able to figure out which way it is aligned. And the spring is so thin it's easy to lose in the driveway.

Good luck.