You'll need to replace the glue tape. They come with none. I'd clean all the old off, and install new. Put it on the door where it should be, and heat it up with a heat gun, or a hair dryer to make it soft. Press the barrier firmly in all areas to seat it. Heat the barrier again, and press it more to make sure it seals.
IMPORTANT: If there are any small areas that don't seal, water will find it-which is why you need to get the old stuff off. Double layering will leak. The bottom is the most important area, and about midway up the side for good measure.
I think the adhesive is some sort of butyl tape. For good measure, you can silicone the bottom of the barrier after you install it.
I hate that job btw. Barriers suck. It sucks that water enters the car.