can't change serial port

I am using IDE 1.8.1 with a arduino clone, windows 10 and when I try to change serial port (to com4) the port option is greyed out and dosen't let me click it. please help!

How do you know that the device is on com4?

I checked in device manager

Shut down your IDE. Unplug the Arduino and start over again. This has fixed this issue for me in the past. sometimes you may have to restart your computer as well.