That looks like the weather stripping. You should be able to just remove that one side, buy a new piece and put back in. Don't know the exact style you have until you pull it out and then you just find the matching kind and put back in. It looks like the kind that just is installed in a groove so you start at the bottom or top and pull it out. Or in the middle as the video shows.

Here's a video that might be useful

https://www.todayshomeowner.com/video/replacing-weather-stripping/

Q-lon Weatherstrip is all that is by the appearance. Should be available at any lumberyard or home center.

That's weather stripping. All they need to do is pull it out and replace with a new piece.