first you need to know how to communicate with pc using serial port, I have a laptop pc and it has no serial port so I dont know how to use serial port.

but you can search on this foorum,there are lots of examples about it.

you can send A10 or C10 to the pic with serial port, and the pic will select the counter according to the info that you send.

And to understand when the counter finish count, you should find a solution.
Does it informs you when it finish counting?