getting json from b3dm files

1. A concise explanation of the problem you're experiencing.
i have tried 3d tile tools and one online json convertor ,althought i got the json file, but unable to plot it on the globe. we even tried to change one already build json code, but it didn't worked.
so can anyone tell me, how to build my json file

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.