This set-up can be done by a user with Super Admin access.
Click My Roles > Company Settings > Settings. Locate the setting that is labeled "Set default lead owner?" and make sure it is set to "Select Option"
Click down to the Appointment Types tab under company settings and then click +Add New in the top right corner:
Scroll down until you see the "Auto scheduling rule" and select "Round Robin"
Be sure to click "Save Settings"
This setting will affect all leads created after the change is made. Once an appointment is set on the lead, the round robin assignment will work.