webdesignwala were you able to access the installation page where MySQL credentials are asked ?
The cross origin error would usually happen after a successful installation if you access the forum using the wrong canonical URL. During installation, the URL used at that time will have been copied to
config.php. You can edit that file to adjust it if you need to replace http with https or change the domain name. If your website is accessible though both apex and www subdomain you will have to choose one and setup your own redirects to prevent the wrong one being used.
If that doesn't help, can you share more details about your hosting and maybe your website URL?