Use only the manufacturer's stated alternative operation, if the model provides one. An unrelated magnet or improvised knob is not an acceptable substitute.
What the observation means
Some designs use a removable control for particular functions or locking behaviour. Its absence can affect the hob differently from a damaged touch panel.
A useful next step
Identify the exact accessory and obtain compatible replacement advice. Do not force a substitute onto the surface or enter hidden settings to bypass the missing part. If the normal controls cannot reliably stop or adjust heat, leave the hob unused.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.