What first step should you take to change the end date for multiple line items while using structured data files (SDFs) to make bulk edits in Display & Video 360?

To make bulk edits using SDFs, you must first download an existing SDF from Display & Video 360. This downloaded file contains the current configuration of your line items, including their end dates. You will then modify this downloaded file with the new end dates and re-upload it. Uploading an updated SDF before downloading one would mean you're trying to modify data that isn't yet in the correct format or doesn't reflect the current state of your campaign. Making changes directly in your Display & Video 360 account or directly to an SDF within the platform are not the methods for bulk editing via SDFs; SDFs are designed for offline editing and re-upload.