You need to look at the database settings in the file and make sure they are valid.
If you don’t know how to do that, ask your web host.
If they won’t help you you need to find another web designer.
Anyone with WordPress experience will be able to help you as the functionality is virtually the same as WordPress.
Remember NOT to show the password in that file to anyone you don’t trust as they will then have read/write access to your database.