Hi Sihan, I hope you're doing well!
There's two methods for enabling the Debug UART in the MCUXpresso IDE:
- It can be enabled when importing the project by choosing the following option in the example selection window:

- After the example project is imported, the debug UART can be enabled by selecting this option in the Quick Start Panel on the MCUXpresso IDE:

Regardless of which method is followed to enable the debug UART, the pins used for it (FC0_RXD is GPIOA17 and FC0_TXD is GPIOA16) are mapped to the Debug USB port, which allows the user to connect to the debug UART with the same USB cable used to debug the project.
Please let me know if you need any more information.
Best regards,
Sebastian