How do I get the control knob off?

I have a Mira 722 mixer shower which is over 20 years old. I am trying to strip it down to service it, but cannot remove the flow control knob which seems to be stuck fast. Can anyone suggest the best way to get it off?
Natasha, August 2022


done
https://m.youtube.com/watch?v=MnTfj-8vA_Y

Wjedjh, August 2022
link Click here to see other fixes for Mira 722.