I know this is a very old post, but I am having the same issue in the same tutorial.

The notebook is accessible from within Mathematica, and the file is located under the following path on my hard drive:

/Library/Wolfram/Documentation/13.2/en-us/Documentation/English/Paclets/PDEModels/Tutorials/Acoustics/ModelCollection

The code in the RoomEigenfrequencies notebook includes a relative reference to another directory called "SupportFiles" but this does not appear to exist on my hard drive:

bmesh = Import[FileNameJoin[{
ParentDirectory[
NotebookDirectory[], 6], "SupportFiles", "SmoothWallModel.stl"}], 
   "ElementMesh"];

I downloaded the "Mathematica + Documentation" installer, which I would have expected to include local copies of all example notebooks and supporting files.

Any help on how to add the "SupportFiles" material will be appreciated.

Edit: I do get the "Evaluate Initialization Cells" popup mentioned above, but clicking ok does not address the issue. It seems like the files are nowhere on my hard drive.

Edit: Realizing this question relates more to Mathematica than to Wolfram Language, I posted a new topic under the Mathematica group. Apologies for the duplicate query but I figured it should be posted in the correct group.