Only attempt to this repair if you are licensed to do so. Working with natural gas is dangerous. Please call your local gas company or look up a repair man in the yellow pages.
Find a replacement valve. Make sure the new valve is physically the same. Locate the supply and turn it off. Using a union as a starting point, unthread as needed.
You have to remove the top panel of the cooker and lift up. Then you can see the place where all the gas valves can be fixed. Remove the old and fix the new.
