Code goes into Page Footer Code (body)
Custom code in head and body tags - Webflow University Documentation
Read-only Webflow - Flat Surface Shader BG Demo
What you’re customising is actually the fourth script. In that case you’ll have to host your changes elsewhere and replace the fourth script with it.
Here’s how
How to host text files on Github
How to embed files hosted on Github
Also, feel free to contact me for further code help and/or customization of third-party plugins