Configuration of Label - Sample modifier

I'm trying to get familiar with OrcaSong and OrcaNet. I have already trained some models and everything is working fine. Now I would need to filter my train dataset (already concatenated and shuffled), and exclude events from the training based on their 'y' value. I saw there are some possibilities of doing it exploiting label &/o sample modifiers, but I don't really know how to configure them. Any example somewhere? I also tried to "manually" mask the dataset but something went wrong.

Thanks for the help