There are plenty of threads on the forum about not seeing the addon manager menu: if you searched the forum, you would probably found them.
However, check the following:
- Did you had any error or warning messages during installation ?
- Did you get a request to trust the Addon Manager module as soon as you started FSX the 1st time after you installed LSZH ? Have you replied "Yes" to both questions ?
- Can you check if the Addon Manager has been added to your DLL.XML file, located at %APPDATA%\Microsoft\FSX
- If you mistakenly replied "no" to any of the trust request you should have had, you can try resetting the request, by editing the FSX.CFG file, located at: %APPDATA%\Microsoft\FSX. Look for ALL lines with a bglmanx.dll reference, and delete the WHOLE line. Save the file, then launch FSX again and check if you get the trust question. Obviously reply Yes to both questions.