Help with Database Not Found Error After Site Migration!

[Frappuccino]

Hello Dear Friends, The issue at hand is not related to me. I'm not exactly sure how to explain the problem, but I will try to explain it somehow. Now, a friend is managing a local news website. This site was obtained from a developer X (made from WordPress). The database connections are normal. The database name, username, password, settings in setting.php, and all settings in Sql are fine. The site's URL address and so on. The problem is; When I talked to the friend who gave me this script, he claimed that there was an issue due to the PHP version. The PHP and MySQL version of the script is 5.6, while the hosting is 7.3. But I have downgraded the version to 5.6 via MultiPHP Manager. When we try to log in to the site, I receive an error message saying "Database Not Found." If anyone can help with solving the problem, I would be very happy.