You cannot convert any 7-zip archives (.7z) to ISO format (.iso). However, you can create ISO image from the files within the 7-zip archive or put the whole archive on the image. Some programs may also offer the "direct conversion" of 7Z to ISO, but it basically just automates the process and does not actually convert anything.
Sometimes people want to download ISO images from the Internet, but get .7z archive instead. You do not have to look for conversion, just extract the content.