SyncTrayzor needs to be the service which starts Syncthing, because it needs to pass the API key to use securely to it on startup.
Syncthing will auto-update however, and by default it will use the same database location as Syncthing would use if you just ran it yourself (if you’re using the installed version of SyncTrayzor that is, and not the portable version). So all you need to do is to disable whatever mechanism you set up to run Syncthing yourself, and let SyncTrayzor start it.
(If you really want to use a syncthing binary that’s in another location, you can set that in the settings, but SyncTrayzor still needs to be the thing which starts it).