Remove the handle, remove the bonnet nut, remove the diverter stem, replace washer.

Is that valid for a built in shower valve like the one attached too (it's not an identical match to the exact model I have but is very close - both are Ideal Standard)? What should I be looking for if I manage to remove the metal face plate please? What sits behind?

Thanks

You should not piggy back on someone else's post. Start your own thread.

Pull out diverter, if there are flats surfaces on the diverter (hidden by the pull knob when in the closed position) unscrew the diverter from the valve.