Hi,
1. You can login from https://sustainablesarah.uk/wp-login.php or if you lost the credentials i would suggest to recover or change the login info from Hosting>cpanel>phpmyadmin>YOUR SITE DATABASE NAME>wp_users Table. You may take help from this article https://www.bookwebmaster.com/wp/get-wordpress-username-and-password-from-the-database/
2. Maybe you are talking about quick installation WordPress link. If you reinstall wordpress from the domain manager, yes it will replace your website content.
Regards
FaithCoder
