How to replace missing knob / buttons on my Shacklock Chef wall oven?

The top larger knob (& spidle) that turns the light on in the oven is missing. I can see from the existing bottom knob that this sits on a white spidle, I dont know for sure but and it looks like it could be inside behind the panel plate. I am hoping not broken. How do I access this area? - is it possible to remove this control panel area - it seems to be that the oven would need to be removed from the cabinet for access?

Another smaller 'push button' type (one of 5) is also missing. This sits on a metal spidle which is still there. My new part has both the metal spidle and the button. I dont want to break it as these parts are hard to find. My question here is does this need to be replaced as one unit or can the 'button' part be pulled on and inserted on the existing spidle?

Grateful for any advise you can give. Thanks in advance