If your database connection is wrong you will get an error says
Error establishing database connection so if you seeing login form your connection is fine and wp-config has nothing to do in your issue.
If you don’t remeber what’s your credentials are, go to your database manager like phpMyAdmin and look for _users table and take a look what accounts are in your WordPress installation. If you don’t remember your password there is simple way to recover it from database. Edit selected user and type new password in the password column and set type field to MD5. Then your password will be pre-reset. When you’ll try log in with your new credentials WordPress will hash new password.