1 answer
To update the particular Record line items, you need to have a unique Record ID field for that object, so that the data from the jitterbit file can be mapped to the records.
Steps:
1. The file you are uploading from jitterbit should have unique record id field for each record.
2. Write an Apex Batch class to update the data by mapping the parent records Unique Record Id field.
3. Fetch the line items of that record using Unique Record Id field and update.
Thanks