loose (now fallen off) oven knob?

I have a an oven/grill unit built into the work surface in my kitchen, for a while the knob to turn it on and changed from oven to grill has been loose, making it hard to do so, the problem increased and now the knob has fallen apart.

I Know how to fix this part, but I need to remove the panel at the front of the oven in order to access the main part of the knob to fix back in place.

can anyone tell me how to do so?

it's a servis brand oven