To optimize the domain decomposition for MPI2D, I need to precise the bathymetric file to the "decoupe" program. Where do I get this file ?

Firstly, since the file must be a netCDF file, define l_bathy_save=.true. in your paraspec.txt, run the code a few seconds, and it will save the bathymetry (H0,HX,HY) into the file. This bathymetry is the one you use throughout the simulation.
Secondly, rename as bathy_[CONF].nc