It is held on with plastic pins attached to the chrome metal strip and go through plastic sleeves in the body. Get a tool, such as a wide putty knife, and slip it between the body and rubber seal at one end. A screwdriver may work but is more likely to damage the trim, and you need to get right next to the pin. Then carefully pry away from the body. It will snap out. There are several of these pins along the length of the trim. You probably should replace the plastic sleeves before installation (cheap part). The pins will snap back in with a soft mallet or even with a tap from the palm of your hand.

Don't want to scare you, but when you start seeing rust coming out from behind parts, be prepared for a lot more rust and possibly holes behind the part.