Since this is in Germany, I would assume the following (this is a very common situation):

* Behind the current oven+hob combo, there is a box on the wall with five wires and three-phase service ("Herdanschlussdose"). Currently, the oven part is connected to this box, and the hob is connected to the oven (which containts the buttns to control the hob). In the panel ("Verteilerkasten"), there will be a dedicated 3-way fuse for this box.
* It is likely that your new separate oven can only needs one of the phases and the induction hob can use the other two, but you need to check the manuals. You can do that directly at the Herdanschlussdose, or you can buy "power splitters" (such as this one: https://www.reichelt.de/kuechenanschlussbox-herdanschlusskabel-2-2-2-m-heit-500580-p277242.html) which already have a separate outlet for the oven.
* If you need to ask, **it is certainly better to have an electrician do the work** -- ovens and hobs are the most powerful electric devices in your typical home, and mistalkes can kill you, burn down the house or destroy your devices. I'm not sure about the law, but it is possible that you are not even allowed to do such work.