WARNING: This page is about a different car, the 2005 Chevrolet Optra5 and 2005 Chevrolet Optra. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: View Of Head Restraint And Guide Sleeves
Courtesy of GENERAL MOTORS CORP.
Install the guide sleeves into the seatback and press them down to engage the guide sleeve retaining latches.
Install the head restraint into the guide sleeves.