Hello,
The demo creates a wireless IEEE 802.15.4 link between the UARTs on two JN516x/7x devices. I have been looking in our available examples and that it's the closest application note to what you are trying to achieve, you will need to create the application by using that as a base and adapt it to your needs if what you are trying to do it's a wireless UART.
Sorry for the inconvenience this might cause you.
Nonetheless, when you mention wireless UART, what are you exactly looking for? Just to see the message on the rest of the serial terminal of the devices? is it like a chat?
Regards