Every 13a oven I have seen comes with a standard 3 pin plug, that’s why they make them with the lower power requirements so you don’t need a dedicated cooker circuit and they can just be plugged in. That is a small sample mind.
As you already have a piece of 6mm going from the termination point to the existing oven, just disconnect it from then existing oven and connect it to the new one of it needs to be hard wired. Ovens that need to be hard wired don’t normally come with cables and you need to supply your own.
If you are not sure, get an electrician or ops for the companies installation service and they’ll make sure it’s safe.