Hi @adeliab,
As explained in this topic, the @@config@@ construct is a placeholder that will be replaced by the runtime. The information contained within this value will be provided automatically by the runtime based on your configuration and also possibly based on parameters received from the client application.
In the Lock default template, this value is stored in the config object. If you are using the Classic Universal Login Experience with the Lock template, you can view the data in the config object by typing config in the browser console.