I’m not familiar with that course, but in all the other courses I’ve seen here the utility functions are included in separate python files packaged with each assignment. There’s a topic on the DLS FAQ Thread about how to download all the files in any of the assignments.
If you just want to look at that individual file, click “File → Open” from the running notebook. That will give you a file explorer view of all the associated files. Look for the file w3_tools.py.