The serial number will not be assigned to the serial port until the computer is connected to the serial port device. You can check it on your computer. You can right-click my computer and then "Manage"-Hardware Management-Universal Serial Port to see if it is COM. If there are several, unplug the one you need, see which one disappears, and then plug it in, which means it is it. Then set it to the corresponding serial number in the serial tool.