Something is stuck at the desk and describing it on the phone is slower than showing it. Download the assistance client, run it, and read the code on screen to the operator you have on the line.
Nothing is installed. The file opens a single window with a code in it and leaves nothing behind when you close it.
Tell the operator the code on the phone. Until you do, nobody can see the machine — the code is what opens the session.
Closing the window ends the session. A new one needs a new code, read out by you again.