DFR0205 How do I get this to give me 8 V.D.C at 3 AMP with 20 V.D.C. input?

I have bought a DFR0205 DC-DC POWER MODULE 25W.    I need to connect in to a 20 V.D.C. supply and need 8 V.D.C. at 3 AMPS output. What do I need to link up or additional components needed to achieve this using the DFR0205 DC-DC module?