In order to answer your question, you should try to observe the lowercase and get to 'localhost/phpmyadmin'. The PHPMyAdmin usually has a tendency to have inconsistent directory name data on all the versions available. Then you must confirm the URL by searching and verifying the name of the root folder and if the config is the initial problem, then you should be getting a PHP Error and not that of the ‘Object Not Found’ Error. However, to solve the config Error, you must confirm the case which your PHPMyAdmin is located in and that the root directory is where the config.inc.php is located. If the steps mentioned above is exactly how you are proceeding, then change the name of it to something as a backup and then copy the config.sample.inc.php which is in the same directory and then finally, change the name to config.inc.php. This should help it work and if so, then click and open both the config.inc.php and the earlier backup taken.
After an analysis of comparison, copy and paste or change the important parts which you would like to carry over. In the default state, the file is not very lengthy and should be relatively calmer to do so. Please Note: If the cause why you one wants the previous config is due to the setup of security which was present earlier, then the suggestion would be to use the wizard security inbuilt into the XAMPP. This will assure you that your version and configuration is on the same level or that the configuration is for the correct version but there is still no assurance about various XAMPP/PHPMyAdmin versions implementing the safe services or security in the exact same manner.
XAMPP Security Wizard