Keep it safely aside and photograph where it was found, without reaching into the appliance to look for more. A fragment may come from food packaging, an accessory or another object; its origin should not be guessed.
What the observation tells you
Do not glue it back, discard it immediately or run the disposer to see what is missing. If it resembles part of a protective baffle or the appliance has become noisy, stop use until its condition is confirmed.
A useful next step
Show the fragment and the location photograph to the engineer. Its size, material and broken edges can help identify the next inspection without dismantling the unit beforehand.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.