help me to connect Weighing indicator to arduino via usb

i change rxpin and tx pin to 2 and 3 but nothing change.
my code can read data 8 data bit 1 start bit from PC to arduino and my weighing* can deliver data to rs com using 8 data bit and 1 start bit.
how to connect my weighing* to arduino using rs232?

*my weighing is And EK-300i