Know Who’s Who with Case Contact Roles
Where: This change applies to Lightning Experience in Essentials, Professional, Enterprise, Performance, Unlimited, and Developer editions.
How: To set up case contact roles, from Setup, enter Case Contact Roles into the Quick Find box and select Case Contact Roles. Click New, and start defining the contact roles that are most useful to your org. Then open the Object Manager for Case in Setup, then edit the case page layout and add the Contact Roles related list.