How to run only a subset of your Mesh ?
 

I am new to OpenFoam,

I have a Mesh (representing 2 layers) and a running model.
I would like to run the model in 2 phases.
Phase 1 : Make bottom layer inactive and I only run the top layer
Phase 2 : Make the top layer inactive and continue running with end of phase 1 as boundary conditions for the topwall.

Is there a way to inactivate a set of cells of the Mesh ?
How do you do that ? And what about the Boundary conditions ?

Thank you