What is a "220v core"???
The dryer is a gas dryer that has a standard 120V cord and plug?
And you have a "240v" dryer receptacle and circuit on the wall?
This is not a simple swap out. If you are experienced in basic electrical work you can probably do it, but if not PLEASE hire a pro. This involves splicing #10 wire and working in a live electrical panel.
Im not an electrician but Im wondering if you could cut and marrett off one of the hot (black) wires, then use the other hot (black) on one side of the plug (brass) and the neutral on the other side? And of course use a ground. From what I have learned, 220 volt consists of two hot 110volt wires, a neutral and a ground? Can someone verify this?