Black triangle trim on rear door

[Jay1710]

Hi, I have a 57 plate Audi a4 slime, the black triangle trim on the rear door is peeing and looks awful, I have managed to find a trim which are apparently really hard to find nowadays but how to change it? I have seen a few videos but none show to to do it on my car, some say it’s a massive job others say it’s a quick fix. Any help would be appreciated 

[Steve Q]

Please could you take a pic of the trim and where it fits.