Crosswater concealed controls

[DarrenF]

Hi, not sure of model but it seems to be the 3 square type taps/valves like cross water controls for my shower. How do you remove the square control knobs?
There seems to be no little grub screw any where on each of the square knobs and I have tried to see if they just pull off, but no joy.

Any help much appreciated.

Thanks in advance.