Transformation of LOD(Level of Detail)

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:

If you’re talking about terrain or imagery you can set the same property on the globe

Does that answer your question?