You can't install 7-Zip without admin privileges, that what the problem is? You can try using a portable executable, for example, this one. Open it, navigate to the location where you downloaded `pa08_0016.7z`, open it, and extract it using the "Extract" button in the top left corner (don't drag & drop into the File Explorer). Alternatively, the access to Microsoft Store usually doesn't require admin permissions, so you can try downloading NanaZip from there.