Hi.
What do you mean?
I’m not sure that I understood your question…
Do you want to download version 3 of the eBook?
You just need to access the eBook page and download the eBook from there: https://rntlab.com/module-1/learn-esp32-welcome/
 
It doesn’t include information about UART.
For that, we recently created a free tutorial that you can read here: https://randomnerdtutorials.com/esp32-uart-communication-serial-arduino/
Regards,
Sara

Thank you for your response
Roger Lakin

Let me know if you need further help.
Regards.
Sara