Hi I have just replaced all the rubber seals on my car, and if I am reading your thread right it’s the curved piece on the roof its self you want to replace.
Take the roof off and turn it upside down there are two screws one at the front and one at the back undo these and peal back the rubber from the roof it has some black adhesive to seal it against the roof , the rest is held in to two channels which just pull out. When you buy some new one’s the black adhesive is already on the rubber, and it is just a matter of feeding it back in to the channels and replacing the screws.
Hope this helps…