adding new field in the response of occ v2 service

Hi, i have a requirement like need to add thumbnail image in catalog service response this is the service i am using for getting catalogs https://localhost:9302/rest/v2/apparel-uk/catalogs please suggest me the steps required for adding new field to the occ service response.

NOTE:i have this thumbnail attribute for category in hmc but it is empt.same present in the categories table.i added the image in hmc it is not getting reflected in the response.i did indexing also.