This lab has an admin panel with a flawed multi-step process for changing a user's role. You can familiarize yourself with the admin panel by logging in using administrator:admin.
To solve the lab, log in using wiener:peter and exploit the flawed access controls to promote yourself to become an administrator.
Log in using the admin credentials.
Browse to the admin panel, promote carlos, and send the confirmation HTTP request to Burp Repeater.
Open a private/incognito browser window, and log in with the non-admin credentials.
Copy the non-admin user's session cookie into the existing Repeater request, change the username to yours, and replay it.