I'm very stuck trying to do what should be a simple maintenance item. I need to replace a worn shower diverter valve. However I cannot - for the life of me - figure out how to remove the pull out knob so that I can remove the face plate and remove the valve. I assumed there would be a screw behind the cover "button" to remove the knob - as with the hot/cold valve... but that's not the case. See the photos for more details.

The unit is branded SOHO and matches the rest of the bathroom hardware. Its nice enough and well made but challenging to maintain as its as though the brand never existed. I've been able to replace the faucet cartridges but only via a couple online suppliers that sell a Kissler replacement. Assuming I can figure out how to remove the diverter, I'm hopeful that the same supply houses have the valve.

Thanks in advance for any suggestions. I'm hopeful it's something stupid simple thing that I've overlooked. :)