Right after Efficy 11.3 installation you should see the "Create Database" button on the Designer logon page.
If you check the HTML code you'll find that the "Create Database" button on the logon page is put inside a "<%OnSelectCustomer()%>" tag.
This OnSelectCustomer() function checks for two things:
1) If the Efficy.CustomerSelection setting (in ServerSettings.json) is empty, it will allow the contents (database creation button and customer selection dropdown) if there are no customer profiles defined. This is the situation directly after installation on a new server.
2) If the Efficy.CustomerSelection setting is not empty, it will allow the contents if you have passed this same value in the URL as parameter "customerselection". You could call this a sort of "password" for showing the database creation button and the customer selection dropdown box.