If you mean the strip along the front edge of the rear quarter window, it comes fixed to the glass, so you would need to buy another window and fit it.
It is a very involved job removing and refitting the window. First you have to:
Place the vehicle in cabriolet position.
Remove :
The rear seat
The rear seat back rest
The rear quarter panel side top trim
The rear quarter panel side trim panel
The rear quarter panel loud speaker
The front seat belt
Rear quarter panel exterior weatherstrip
Rear quarter panel interior weatherstrip seal
The air seal sheet
The water seal sheet
Then you can start removing the window.
The illustrated procedures are in the Peugeot Service Box Documentation, and the
emanual.