Sorry, but that's not possible. When you did this (if you did it, of course...)
- Reply YES to the question "Do you want to remove the Addon Manager ?" and "Do you want to remove the Couatl engine ?"
The uninstalled removed the WHOLE fsdreamteam\couatl FOLDER from FSX and, since the current installer comes with the 3.0 version, it's not possible the old version came out again.
Unless you have skipped that step AND the antivirus is STILL interfering. OR, you *downloaded* the 1.9.12 installer, but you have launched another one. As I've said, check the version number of the installer which is displayed WHEN THE INSTALLER STARTS.
And again, please be sure you do ALL the steps I listed before. Do not skip ANY step. After the uninstall, check if the fsdreamteam\couatl has been removed, which is what the installer normally does.