A knob that no longer selects reliably needs model-specific assessment. Its pointer may not match the actual programme, making the intended treatment uncertain.
Understanding this situation
Do not force it, use pliers or assume the previous position remains selected. On some models controls behave differently, so an appearance-based adjustment can choose an unsuitable cycle.
A useful next step
Keep the machine unused if the setting cannot be confirmed safely. Provide the full model and describe whether the knob turns, slips or has detached. Do not order a visually similar control without checking compatibility and the cause of the damage.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.