You may need to use ODBC driver to connect to IBM iSeries DB2 (AS/400) systems.
Go to IBM site and download IBM i Access Client Solutions, for example, IBMiAccess_v1r1.zip. Additionally download IBM i Access Client Solutions - Windows Application Package, for example, IBMiAccess_v1r1_WindowsAP_English.zip
Run the installations, and ODBC Driver will appear in your system: