How to show UART message

I am buy MediaTek X20 board and sensor board.

and connect sensor board with X20 board
and plug usb cable to USB port on sensor board. (sensor board translate UART to USB)

I Expect u-boot and linux booting log.
But nothing printed on COM port.

How can I see booting message of X20 board.

The X20 differs from the most of the other 96Boards products both because the console the image uses by default is running on LS-UART0 (instead of LS-UART1). It also has very fast default baud rate of 921600.

Thanks.
It’s working.

Sensor Board translate UART1 to USB. (ignore UART0)
so I connect X20’s UART0 to Sensor Board’s UART1.