Hi Aarati,
Actually, approved change requests are an input to the Direct and Manage Project Work process (page 93 of the PMBOK® Guide).
As far as approved change requests as an input to the Control Quality process, there is a good description on page 301 of the PMBOK® Guide. As an example, let's say that a project deliverable was found to be defective, and a change request was submitted to repair the defect. Once approved, the approved change request might be used as an input to the Control Quality process to ensure the defect repair was performed in conformance with quality standards and the repaired deliverable passes any applicable quality control testing.