In most cars if you take the door card off then you should be able to see whats holding it on. But every car is different, also don't cut the rubber boot and tape it back up it will never be water tight and in the long run will have problems with water corroding the electrics.
Looking at what little we can see in that video, it looks like it'll just be held in place by molded ends. Reach inside the door, and squeeze the tube which protrudes, while pushing it out.
