The four prong plug needs connections for:
Ph. A, (Black wire), Ph. B,(Red wire),
Neutral,(White wire), & Ground, (Bare wire).
Chances are good that there are wires in the
wall box for all of them.
Check the box. 'Betcha' there's a capped white wire there.
Just buy & install the proper receptacle.
(Blk. & R to brass screws, white to silver screw,
bare to green screw).
Some fool may tell you to connect the neutral
to ground or vice versa. - Don't.
Retired Electrical Consultant