Hi.
As I wrote, the parameters.php file should also have been transferred and then the information about the new database changed in it. If necessary, you need to take the cookie key parameter from the original file. Why can't you log in? Because the cookie key is different. The password check is md5 consisting of the cookie key followed by your password. The next thing that is needed is to change the .htaccess file. It will contain links to the old subdomain.