If it's a built in oven, -Turn off the elecric at the mains.
Open the drop-down door.Unscrew the all the screws that are facing you. Pull out the oven box from the built in unit - keeping it level. (be careful as very heavy and you will still be connected to the main gas at the back - you'll need help) Unscrew the screws on the top of the oven. You can now get access to the back of the knobs.
Lesley
November 2008