After an order is completed, Customer can request for a warranty, refund, cancellation from the customer account dashboard → Orders (Picture below).
Once a customer click on Request Warranty, he will find out the form that was created by the admin (an example form shown below).
The item needs to be selected by ticking on box.
The request type is the first to choose among the options available (Replacement, Refund, Cancel & Refund as a Store Credit). Refund as a Store Credit come only on Pro version.
After choosing the request type and the other forms, hit Send Request will proceed the request.