1. Check the concave part of the felt lantern for cracks, and fill the cracks with glue first.

2. Carefully polish the concave part with fine sandpaper. After polishing, put the lantern outdoors to dry, so as to avoid damp and mildew in the concave part.

3. Wipe the lantern with a rag dipped in some detergent, and be careful not to damage the lantern.

4. Applying some lubricant to the depression can increase the elasticity of the felt lantern and restore it to its original state.