How to transform LOD3(Higher level) Data into LOD2,LOD1(Lower levels)??
What kind of data do you mean?
If it’s a tileset, CesiumJS will automatically refine to lower levels depending on the computed screen space error, which I believe is based on a number of factors including the distance to the camera. You can adjust the value here to get it to refine sooner: https://cesiumjs.org/Cesium/Build/Documentation/Cesium3DTileset.html?classFilter=Tileset#maximumScreenSpaceError
If you’re talking about terrain or imagery you can set the same property on the globe https://cesiumjs.org/Cesium/Build/Documentation/Globe.html?classFilter=GLobe#maximumScreenSpaceError
Does that answer your question?