Service relationship management is the joint activities performed by a service provider and a service consumer to ensure continual value co-creation1. It involves establishing, maintaining, and optimizing the service relationship throughout the service lifecycle2. Service relationship management ensures that service providers and service consumers continue to create value together by aligning their objectives, expectations, and capabilities3. References: ITIL Foundation - ITIL 4 Edition, page 5; ITIL4 - A Pocket Guide, page
16; ITIL4 Practice Guide: Service Relationship Management, page 7.

Reference: https://www.bmc.com/blogs/itil-incident-management/