If i look at the schematics, you need to remove the current jumper wires, and make a new jumper wire;
(Note 3; "Only the one shown with a dashed line is connected for 220 V.A.C. operation.")
remove Jumper wires that bridge connections 2 & 6 and connections 4 & 5 on the 12 pin connector.
Install a Jumper wire to bridge connections 2 & 5 on this plug
that will connect transformer connections 3 to 5
Then you need to change the fuse and varistor. (note #1 & #2)
Also it might be worth to investigate note #5 because the voltage is no longer 220 Volts since many years but 230 Volts.