I believe you're talking about the rocker extension to the door....
The service manual has a illustration in the body section on page 6J-3

I linked two PFF threads:
remove and install new rocker (aero) panelshttps://www.fiero.nl/forum/...110502-2-095321.htmlRocker Panel Removal on GT https://www.fiero.nl/forum/...110502-2-100009.htmlPFF "GT Rocker Panel" Search
https://www.fierosearch.com...anel&Action=DoSearch------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles
[This message has been edited by Vintage-Nut (edited 04-23-2025).]