i am struggling to find an option for order return manually. if a customer returns order at my shop manually by hand how can i change status or minus some products to return the order in admin side can not see any solution for that..

Merchandise returns may be created from the My Account section by the customer. You can use the "Place order" feature, to login into the user account and make the return request manually on behalf of your customer. You can also use the Web API and integrate it with your ERP/OMS system, where you will manage merchandise returns.