Replacing door weatherstripping

Can you post a photo of the back side of the new seal? Some are held on with plastic clips that have a small hook. Some just have two ridges molded in that get poked into a metal channel. If you have to stuff the rubber into a metal channel, the job will be easier if you spray a little Silicone Spray Lube on the rubber first. That makes the rubber slide into the grooves real easily, then it will evaporate quickly.

If yours has the plastic hooks, they have a round head, similar to a nail head, or a small "T" for a head, that holds it in a small hole in the rubber weatherstrip. The new weatherstrip would typically come with new clips installed already because the old ones will become brittle with age. If you have to transfer those to the new seal, pull the clip sideways until the end of the "T" can be tilted out, then pull the clip out. Insert it into the new seal, then stretch it until the other end can be poked in. Be careful to not pull real hard because those holes can be torn easily. Any body shop and most auto parts stores will have replacement clips if you need them.

I manufactured a sad drawing to show how to remove these hooks. To get them out of the metal body panel, use the seal to pull it out very gently, then you will see the end of the hook peeking out of the hole. That is the tip shown in red. Use a small flat-blade screwdriver to push that hook in the direction of the red arrow. There is usually some ridges on that part too, so you may have to push and release it a few times. The blue arrow is pointing to the head that sits inside the seal.

A different version of this clip uses "feather fasteners", meaning a group of flexible wings that allow the clip to be pushed in easily, but it will not want to come out. There is a forked tool for prying those out. You can also get them out by cutting them with a side cutters, or you can use the side cutter or a needle nose pliers to grab them, then pry them out. If you use a needle nose pliers, it is easy to scratch the paint, so use that as a last resort.

Looks like you will have a channel to push the rubber into. You will need to work it in a small section at a time. Holding it against the channel, then pulling on the weatherstrip to stretch it will help it slide into place. Spraying some Silicone Spray Lube will help it go into the channel. That goes on like water and makes rubber parts slide over metal parts real easily, then the liquid evaporates and leaves a film of "slippery" behind.

The holes in the third photo are for air to blow in while the vehicle is in motion. That fills the hollow seal and makes it balloon up to form a tighter seal.

I call these "feather fasteners", but I think the proper name is "fender plug". They have wings that hold them in place. There's a number of tools for prying these out. The tool in the second photo is from Matco Tools. You can use a simple needle nose pliers too, but the tip can scratch the paint. If you use a pliers, use it to squeeze the plug, then pry it out. If you don't squeeze it, the head of the plug might just fold upward, and it won't pull out.

If the wings aren't damaged, it is customary to reuse these plugs.