No, dont see that.
That's why you don't see anything. Do you at least remember if you had a request to trust it ?
Can you please try this once, Uninstall KLAS, and say it to remove both the Addon Manager and the Couatl engine at the end ?
Then, go to your FSX.CFG, located at %APPDATA%\Microsoft\FSX and open it with a text editor.
Find, under the [trusted] sections, all the lines that have a reference to Couatl.exe inside (it will be a long line with many random characters inside) and remove the whole line, and repeat this for every line that contains Couatl.exe, if there are more than one.
Then, reinstall KLAS, and check you get asked about trusting the Couatl Scripting Engine at start. You need to reply Yes, of course.
If you don't see the Couatl menu under Addons the first time, it's not a problem. Just launch FSX again.
If you still don't see it, then report back.