Hi there,
Please try to press the reset button quickly and you will see RX led(near MCU) blinking quickly. it will enter into download mode. Then check the device manager. If you see the COM port, it shall work for the programming.
Please do make sure follow http://wiki.seeedstudio.com/Seeed_Arduino_Boards/ to install seeeduino lorawan. when you download the code, please select the lorawan and correct port. thanks.
Bill