Click on the Settings menu and choose COM Port. Then choose the desired setting from the pop-out list. If you don't know the COM port number then use the command Com port Detector to determine which one to use.
If your computer has a COM port that is not listed then contact the author to get the program amended to suit your PC.
If you are using a cable with an FTDI chip in it and you have installed the FTDI D2XX drivers then you can use the FTDI cable Detector command on the settings command to choose which cable to use.
The program will remember your settings for the next time you run.