Stop using the appliance and obtain electrical assessment. Scorching, crackling or a burning smell at a switch is different from an ordinary cooking-setting issue.
What the observation means
Do not repeatedly operate a damaged switch or remove its faceplate to inspect behind it. Its condition may involve the fixed installation, the load or a connection, and cannot be diagnosed from appearance alone.
A useful next step
Keep people away from the affected area and follow emergency advice if there is smoke or fire. Give the electrician and repair business the location and observed symptoms. Do not cover the marks or replace only the visible plastic as a cosmetic repair.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.