Hi,
by default serial communication is done over OpenSDA interface. OpendSDA is a serial and debug adapter that is built into several NXP® evaluation boards. It provides a bridge between your computer (or other USB host) and the embedded target processor, which can be used for debugging, flash programming and serial communication, all over a simple USB cable.

If you refer to board schematic you can find a MCU pin connected to OpenSDA

So LPUART1 on pins PTC6/PTC7 is used.
For sure you can use any external UART interface and connect it to LPUART interface you need via I/O headers available on the board.
BR, Petr