WordPress at a glance
function is not described

wp_not_installed() WP 3.0.0

Redirect to the installer if WordPress is not installed.

Dies with an error message when Multisite is enabled.

No Hooks.

Return

Nothing (null).

Usage

wp_not_installed();

Code of wp not installed: wp-includes/load.php WP 5.2.2

<?php
function wp_not_installed() {
	if ( is_multisite() ) {
		if ( ! is_blog_installed() && ! wp_installing() ) {
			nocache_headers();

			wp_die( __( 'The site you have requested is not installed properly. Please contact the system administrator.' ) );
		}
	} elseif ( ! is_blog_installed() && ! wp_installing() ) {
		nocache_headers();

		require( ABSPATH . WPINC . '/kses.php' );
		require( ABSPATH . WPINC . '/pluggable.php' );

		$link = wp_guess_url() . '/wp-admin/install.php';

		wp_redirect( $link );
		die();
	}
}