Hi, you just need to replace the cooker connection plate with a dual connection plate. If you're oven requires a 13a fused supply, then put a 13a FCU or Socket onto one of the 6mm cables you have connected to the dual plate.
I would use 6mm or 4mm to supply the socket, that's just my preference.
Simply because -
The oven wiring is 6mm and i would leave that in place to make it easier to install a more powerful oven if and when required, all that's required is to remove the socket and connect. As i say, that's just my preference.
Kind regards,
DS