PHP Page Redirect for a Undeployed Website

As the final project in my web development class my project team is building a web page for a local gym.

We have the website set so that a sign-up page is displayed if no user is logged in, or an account page if a user is signed in.

Currently, I have the sign up form redirecting to a "creation" page, that processes the sign up request, which we again redirect to either the sign up page, if the sign up fails, or logs the user in and redirects them to the accounts page if the sign up is successful.

Because the website is not deployed, I dont have access to a URL, so I am struggling to use the header() function for the time being. Are there any alternatives? Thanks!