You must specifically right-click on the first file ( .001 ) and select "Extract" or "Open archive" using the 7-Zip GUI.
If you try to open .002 directly, you will likely get an error stating it "cannot open as archive" because the critical "Start Header" is only located in the .001 file. GGIW.7z.002
Ensure you have GGIW.7z.001 , GGIW.7z.002 , and any subsequent parts. You must specifically right-click on the first file (