To open or extract this "piece," you must follow these steps: How to Extract .7z.001 files - Microsoft Q&A
The file is the first part of a split (multi-volume) 7-Zip archive . When large files are too big for a single upload or storage device, they are often sliced into smaller "pieces" with extensions like .001 , .002 , and so on. SG-4.7z.001