Select the port of your USB to serial converter from the Tools > Port menu. If that menu is grayed out or the port of your USB to serial converter is not shown then one of the following may be the cause:
- You may need to install the driver for the USB-serial chip. From the picture it looks like it's a CP2102.
- You may be using a charge-only or defective USB cable. Test your cable on another device to confirm that it works for data.
- Using a USB 3.0 port on your computer may cause problems. Try a USB 2.0 port.