WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Roof Trim Clips
Courtesy of VOLVO CARS OF NORTH AMERICA.
Install:
the clips on the roof trim as shown.
the holder on the roof trim
the end stop
the roof trim.
Press the roof trim until it clicks. Begin from the front and work back.