Hi Li,
If you use TWR-KE18F, just connect the usb port to computer. Then select the UART port which create by the openSDA serial and debug adaptor, press the reset button, and click the Connect button. The tool will try to connect to the board. Baudrate is not important.
If you use your own board, you should connect your computer to the LPUART port which list on page 565 in reference manual.
If the connection can't established, you can make a full erase. Then it will be ok.
Regards,
Jing