This feature is only available on the Multi Scheduler, not on the Single Scheduler
To configure Dimension Titles on the Multi Scheduler, first go to the Calendars tab and find the Calendar record that drives the Multi Schedule configuration. See Single and Multi Scheduler if you are not sure what the Calendar record is.
Once you are on the appropriate Calendar record page, go to the Related tab, and click New on the Resource Titles related list. Make sure the new record is of type Resource Title, as shown below: