I don't know very much about this example, but it looks like it's the first of four steps in a workflow, and you first have to go to this one to get the files in question: https://www.mathworks.com/help/systemcomposer/ug/mobile-robot-workflow.html
At least, that's how I interpret the line of text above the code you entered:
- To access the models and supporting files used in this example, see Simulate Mobile Robot with System Composer Workflow. After loading the example, run this code in the MATLAB® Command Window.
Hope that helps!