Just to explain a little as this is a very new and experimental feature that is not in the main kicad repository ( yet 
) . This code can calculate the capacitance between any 2 nets in pcbnew, using a 3D electromagnetic simulation.
If your board is not confidential, you can upload it and I can send you the result. If you want it to do by yourself, you’ll have to build that kicad branch and the solver.
The results have been tested with simple shapes ( because we can easily validate the result ), but you can use any shape.
There is an ugly, yet simple GUI under inspect -> Simulation
As an extra, you can have some pretty 3D views 
In order to use this branch, you’ll have to install sparselizard as a shared libarry.
You’ll have to build sparselizard by yourself, ( The lastest commit should be fine for now )
Here is a tutorial about how to build / install it as a shared library on ArchLinux:
( It also works on Manjaro )
Once sparselizard and kicad are installed, using the tutorial, you’re good to go.