Do not obstruct the outlet needed for operation. A cover added without regard to the dryer installation can prevent the intended exhaust flow.
Understanding this situation
Pests, weather and draughts should be addressed with an appropriate arrangement compatible with the appliance, not a temporary plug left in place during drying. The outside outlet also needs safe access for any inspection.
A useful next step
If an obstruction is visible from a safe position, stop using the dryer and arrange suitable attention. Do not climb unsafely or dismantle a wall outlet during operation. Explain the change before a performance assessment.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.