To have two VCs, each managing member APs, they must be in separate Vlans. You should be able to simply disconnect one AP from your current group and move it into a defferent Vlan. It will see that there are no VCs in the new subnet and will elect itself to be the VC.
Some users prefer to set the AP they will move back to factory default, using the reset button on the back of the AP, and reconfiguring it with a clean config in the new Vlan.