The leading edge of the belt trim is held with a "shoe" that has a stud. The shoe slides into the trim strip and is secured by a nut on the shoes' stud. Access is eith from the fender well with the inner fenders removed or thru the headlamps once they are removed. The rear of the trim is usually held with a visible nut in the door jamb. The trim is held with plastic retainers and will likely need to be replaced. There is a plastic retainer that is inserted into the body, retainers are then slid into the channel, and then lined up and pushed to adhere.
You will need many of these and suggest looking at the Flying Spares website to see what you're dealing with.
Very misleading IMHO the Corniche only has the lower cill/rocker and bonnet trim held in with the plastic cups and clips. So nowhere near the amount of trim clips needed. There is a metal retention clip on all 3 strips that has a 2ba nut that has to be removed. The front bonnet nut is accessed easier when bonnet has been removed and best trim replaced after paint before bonnet refit otherwise very difficult to access that nut.
You would need a very looooooonnnnnggg arm to get to any trim nut on a Corniche through the headlamp fitting
The lower finishers you do have to get to the front nut, but there should be a small aluminium plate cover screwed onto the rear lower of the fibreglass wheelarch liner which providing you have small hands can just get into remove it.
Personally whilst a pain I would remove the front wheel arch liners as it will make welding up the wing mirror holes much easier.
Steve........who reads what people say