The affected item determines the next step. A replaceable accessory and a damaged appliance surface have different compatibility and repair questions.
What the observation means
Identify whether the mark is actually on the tray, shelf support, door area or cavity enamel. Do not scrape deeply to determine how far it extends. An old tray can also transfer marks onto another surface, so location matters more than a general report of 'a rusty oven'.
A useful next step
Keep the affected accessory unused if its condition is uncertain and obtain model-compatible advice. If the cavity itself is damaged, arrange assessment. Painting over the area with ordinary metal paint is not an appropriate owner repair.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.