You will have to find out the correct ProgId (same as Class String). This is mostly not the same as the name of the class you want to use.

You can find that ID by searching the registry.

When a COM DLL is registered, ProgID-entries are placed in the registry to allow clients and the COM libraries to locate, create, and use classes in the COM DLL. The registry entries for COM classes are located in HKEY_CLASSES_ROOT in the system registry.

The ProgID keys are located at:

\HKEY_CLASSES_ROOT\<progid>
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For example, if you wanted to create a DataBase-Jet-Object from the Jet-engine (DAO, same as MS Access uses), the ProgID for for the DAO-Classes is located at \HKEY_CLASSES_ROOT\DAO.DBEngine.36 (Version 3.6)

In VBScript this would be written as

    set jet = CreateObject ("DAO.DBEngine.36")
    set db  = jet.OpenDatabase("path\to\database")
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So you have to start "regedit" and search for ProgId that belongs to the DLL you want to use.

Update:

The ProgID has one subkey called CLSID. This contains the CLSID for the class, and this is how a ProgID can be mapped to the CLSID that is then used to instantiate a COM class.