Hi Yes - the trim on the video is not from a W209 but will give an idea as to how they are put together. There will be a number of metal clips that the trim is pushed into. The problem you may have is that either the clips are not seated properly or some may even be damaged. Looks like to remove, they will need to be pulled / pried out by using a trim removal tool if you can get one in there. I think taking this out will be relatively easy but putting it back together and lining up all of the clips will be much more difficult and hence whoever has taken if off in the past may not have lined up all of the clips. In addition, you will have wiring to contend with under the trim.
WIS is the mercedes workshop instruction manuals'.