Are you in general comfortable with including different engine subsystems in C++ and working with them?
Because, if so, the docs should give you everything you need:
https://docs.unrealengine.com/4.26/en-US/API/Runtime/NavigationSystem/NavMesh/
If you’re not comfortable working with Unreal Engine source code in C++ from your own plugin, then it’s likely that the real problem you’re running into is “there are a number of assumptions that aren’t spelled out particularly clearly, and there’s ways of references parts of the engine in the build setup files that aren’t super obvious,” rather than anything particularly related to navmesh.