Locate it in ordinary use
Say whether the smell is strongest at the sink, cabinet or nearby drain and whether slow emptying accompanies it. Include a long period without use.
Avoid chemical experiments
Do not mix drain chemicals or assume a strong product is compatible with the unit. The matching manual governs routine care; persistent smells with drainage changes may need the connected waste route assessed.
A useful distinction
A sink smell that appears only after another fixture empties may need a different enquiry from odour around food residue. Keep that timing because the connected drainage arrangement may matter more than the disposer motor.