How to change another set of NavMesh in realtime?

I am NOT going to dynamically modify a particular navmesh.

I have, for example, 3 different levels (I created prefabs for them), and I can bake each one in editor. But how can I load a particular navmesh when I enter a particular level?

Thanks.

I suspect the NavMesh is statically defined - so it’s loaded automatically for your given level, control out of your hands. If you’re wanting different meshes, then define different NavMesh layers, put different Colliders on those layers, and set each NavMeshAgent’s walkableMask to whatever you want it to walk on at that given point in time.