How to access data from previous snaps

Hi Have a pipeline where i get data from a triggered task. For testing and dev purpose, I am reading the data from files as the first step. In one of the snaps i am calling another pipeline to query servicenow after the query I want to use the data which got in the first snap and the child pipeline to perform another action. But right after the call to child pipeline i added a mapper and in the mapper I only have access to the data which returned by the child pipeline and the data that was sent to the child pipeline. How can i assess data from first snap or any other snap