Since you didn't mention the model number, I have to be kind of general.
If you mean the flame sensor or oven cavity thermostat, they are usually located on the top of the cooking cavity, so you would first have to remove the oven from the wall mount if it's an over the range type.If
so, the installation instructions are very handy, and it's best to have
two people since the microwave can be heavy and awkward.
If for some reason you don't still have your installation instructions, you can
owner's manuals and installation instructions
can download owner's manuals and installation instructions for
several brands (including Amana, Jenn-Air, Kitchenaid,
Litton, Maytag, Roper, Tappan, Thermador and Whirlpool) here.
download Frigidaire owner's manuals and installation
can download Samsung over the range microwave installation instructions
You can find links to other brands and find helpful exploded view diagrams and part ordering help here
I recommend that you bookmark that link to your favorites.
Then you can remove the outer cover to access the parts.We're
happy to help you with free
advice and we'd appreciate your thoughtful rating of our answer.