How to add body for different parts of a parsed model by gltfjsx cmd

[AmirHo3einJS]

I've been searching for a solution for a couple of days but couldn't find the right and best resolution.

Here is an image of my model:

As you can see there is a tunnel with a floor and 2 walls. I couldn't find the appropriate shapes for them in cannon. how can I add correct bodies to these parts and make collisions?