It sometimes happens that an update with Odin fails
Odin shows here a failed problem with the COM port.
This Com port is a virtual port that when you plug in the USB cable it is automatically found.
When can sort this problem when it happens?
Firstly go to Windows Task Manager and close all Samsung Kiss programmes that may be open.
Then remove all USB devices from your PC apart from mouse, keyboard, and the USB cable to your phone. If you have a USB hub then remove that too.
Now plug the USB that’s attached to your phone into a different USB port.
That should have sorted the problem and the flash then works.