How to prepare GraphQL JSON result for Import

I am using GraphQL API to get data from System A. The response of GraphQL are json formatted data.

This data has to be imported into System B. For that I have to prepare the json result from System A to import it via REST-API into System B because the formatting is different and some values has to be changed.

What is the best way to do something like that? Should I save all the data in objects, arrays or something and then create a new json file from it? Im not sure what is the best way to do.