Hi, Luis
Pin 1 is an output pin, You can use it to turn on your plasma cutter, Ports&Pins, Output Signals, Output#2, ("Check" Port#1, Pin #1, set Act/Low/High as Needed).
M3 will turn it on, M5 will turn it off, Need to use a small 5 volt relay(reed, miniature or Best a solid state relay}.
Hope this Helps, Chip