If you want to support the site, consider clicking on the following affiliate link: https://amzn.to/4hvIK0L. It helps even if you don't purchase the item. This video describes how to connect an Arduino to your computer, and then, utilizing debug mode on the Nextion IDE, you can examine the serial data being transmitted.
If you enjoy the content, consider donating a cup of coffee at https://ko-fi.com/cheapcontrols