Having ISO 27001:2013 already in place makes implementation of ISO 9001:2015 much easier than starting from scratch. As you probably know, new version of ISO 9001 has the same structure as the latest version of ISO 27001 and this also means that you can use the same processes for common requirements of both standards.
First, identify the common requirements and processes, like determining context of the organization, resource management, internal audit, management review, etc. Since you already have this in lace according to ISO 27001, you only need to make adjustments to comply with ISO 9001.
Next step is to meet requirements specific for ISO 9001, like writing quality policy, objectives, addressing risks and opportunities, determining criteria for processes, measuring customer satisfaction, etc.