Solution:

There is a simple way to solve this problem. 1, Please power off the PC. 2, Short the SW3 with jumper, that will force the board ID to be '0' and baud rate as '9600 bps'. 3, Short the SW4 temporally, that will reset the PCL-752. 4, Power on the PC and you can find the PCL-752 in PCsentry with board ID '0'. And then you can change the board ID with PCsentry.