Hi @pradip27 ,
Thanks for your post and for being part of the Cesium community.
We have a previous thread here that discusses this topic and has guidance on how to clamp KML to 3D Tiles KML clampping to 3Dtiles - #5 by 11115. I think the best course of action is to try to follow the advice there.
It may also be beneficial to create an example using our sandcastle tool https://sandcastle.cesium.com/ of your use case plotting KML on top of 3D Tiles so we can more easily help debug.
Hope the linked thread helps you move forward and please let us know if we can assist with more specific questions.
Best,
Luke