If you'd like to also swap out headrests between your two seats you can do so by finding and pressing in the "secret" button. You can usually see a slight impression in the back of the seat, revealing its location. If not, feel around for it near the upper edge of the seat back.

Press this button in with your thumb while pulling up on the headrest to remove it from the seat.

To install the headrest simply push it in until you hear the lock click, securing it in the seat.