WARNING: This page is about a different car, the 2019 Buick Cascada, 2018 Buick Cascada, and 2017 Buick Cascada. However, it is still accessible from the selected car via links, so may be relevant.
Install the head restraint (3).
Route the cable (1) through the seat back.
Connect the head restraint cable (1) to the head restraint actuator.