how to restrict logins in firebase

Lets say I have 2 platforms, android and web, linked to my database.

The android is for the users to access while the web is for the admins to access. Both web and android shows different information.

How can I prevent the users from logging in to the web and the admins from the app?

Extra info -the users information are store in /users/uid(firebase generated). While the admins information are not stored in the database.