Assistant api Retrieval Tool - retreiving similar items from attached file

My requirement is to extract similar items from the file for the given query.
I am using assistant api with retrieval tool and function calling, and have added a file while creating the assistant.
The attached file is a .json file, uploaded with purpose ‘assistants’.
the file contains {items:[{item}]}
item: {id:string; field1:string;field2:string;field3:string;field4:string;field5:number;field6:string[]}
the assistant is not giving correct items, it creates its own items.

any help here ?