Create a new admin user in WordPress via code. Drop this file in the mu-plugins directory and update the variables, then load a page in WordPress to create the user. Remove the file when done.

create-admin-user.php

<?php

add_action( 'init', function () {
  
	$username = 'admin';
	$password = 'password';
	$email_address = 'webmaster@mydomain.com';

	if ( ! username_exists( $username ) ) {
		$user_id = wp_create_user( $username, $password, $email_address );
		$user = new WP_User( $user_id );
		$user->set_role( 'administrator' );
		grant_super_admin( $user_id );
	}
	
} );