Are you using the free version of Revo if so it will not show 64-bit programs only the Pro version does.
This Advanced Uninstaller PRO: A Swiss Army Knife for PC Users - Completely uninstall any program, even if it has no uninstaller of its own
is almost as good as Revo and works on both 64-bit and 32-bit programs. It is free for noncommercial use.
I would install 7-zip again and either use the above uninstaller or download a free trial of Revo Pro and uninstall with it.