Release Planning is the process of planning a product release, identifying the capabilities that need to be released, stakeholders and team members involved, budget and timelines.
In Scrum, every Sprint enables inspection and adaptation of progress toward a Product Goal. Every Sprint begins with Sprint Planning and results in at least one increment that is usable to customers.
Some teams release increments multiple times a sprint, other teams group features from more than a sprint before releasing to the customers.
Those releasing at least once a sprint, do not need seperate release planning besides the Sprint Planning that already exists.