Making ERPNext Help Videos with Scripting

I’m trying to run the getting_started.js file, but it throws the error shown below. I notice that when I comment out the parts of the code containing the speak function, the code works fine. I want to add a computer aided narration with the speak function to my video, how do I go about this?
OS: Ubuntu 16.04

You will have to change the voice to something that is installed on your ubuntu system. The default voice is ‘samantha’ which is available on macOS.

please can you suggest how I can change the voice on my ubuntu system?