I just figure out that I can output GPIO by using these code:
Chip_GPIO_SetPinDIROutput(LPC_GPIO_PORT, 3, 4); //Set pin direction
Chip_GPIO_SetPinState(LPC_GPIO_PORT, 3, 4, false); // Output low
Chip_GPIO_SetPinState(LPC_GPIO_PORT, 3, 4, true); // Output high
But I still don't know how to use GPIO to trig interrupt. Still need help. Thanks.