How do I create a single restaurant app in java

Question

I'm developing an app for my fast food joint in Java. I need to have a separate application for me as the admin if possible still in Java. I don't know how to go around that so I'd appreciate some help.

I implemented user access levels in the signup section, now the problem is, anyone else can create an account as an admin but instead I only want to be the only one to sign in as the admin. I concluded it's not possible with a single app rather a separate app for the admin.