Limit number of row modified?

Hello everyone, I am currently use coda to dispatch worktask to my housekeeping team.

For example, I have 100 dirty rooms in the system everyday and I would like to assign task to specific 5 maids by 20 each.

I created a user selection and a button that could select dirty room status and select floor , in which the button will modify USER to the user i selected

However, I want to limit modify row to 20 each per user, is there any formula to limit that? because I want to select all dirty task and do one click to assign 20 each

There for sure is!

Any chance you can share a dummy doc so the community can help you out?