Hello,
let me introduce a tool to create and edit CZML documents.
https://vision.space/cesium-kml-czml-editor/
It allows to create and edit some of the common entity geometries, gives you a nice preview of imported KMLs, and allows to tweak and fix imported Entities look and feel.
Here is blog article with a little bit more details: https://www.endpoint.com/blog/2020/12/21/cesium-kml-czml-editor