When you want to rollback object changes you open the Rollback Objects window. Using the Rollback Type you can rollback to a certain date/time combination, for a specific project or specific transport. Go to Source Control > Rollback Objects.
Date/Time - Enter a date/time combination in the Rollback to field
Project or Transport - Enter a project/transport number in the No. field
Object Manager will retrieve all the objects that were changed since that date or for that specific project/transport. Press Rollback to execute the rollback.