If you want to start small — for example, to test OneDirectory with a handful of users before rolling it out — you have a couple of options.

Use Include specific domains only in Directory Console → Data Sources → Filtering Rules to show only accounts from a chosen email domain. See How to create domain-specific filtering rules.

To limit the directory to a specific set of test users (rather than a whole domain), contact OneDirectory Support and we can help set this up.

Understanding Filtering Rules · Managing your data source and running a sync