I'm sorry, I believe this resource is no longer maintained. Maybe this is not the right place? But how can we create new dungeon plans? Like the N.map included in this plugin?

Do we have to use a software ? Can we make it IG? I think I didn't understand everything

I received your email earlier, I'll copy/paste what I sent earlier.

The plugin has mainly been taken over by RaNull on Spigot. https://www.spigotmc.org/resources/catacombs.73564/
Last I knew, the plugin was mostly working in MC 1.15.x. Some bugs, mainly with traps and hidden doors. I do not believe he has resolved the issue. I suggest hitting him up on the above plugin's thread area.
All the creation and management is done in game. There is no manual map editing. If you plan to rearrange chests, traps, hidden doors, etc., you can do this with the catacomb suspended, and edit within the catacomb's boundaries.