How to enable "Auto add reviewers to pull requests" when a fixed keyword found among the files

Hello,

Am in process if introducing an event “Auto add reviewers to pull requests” (script event handler) whenever a keyword say “xyz123” found/introduced among any of the files in the subfolders similar to pathsMatch method.

However, i could not find a right way to do this.
Let me know in case of any inputs.

Thanks