Add an edge to a surface

Hi there, how can i add a point to a surface (a sort of rebuild, maybe) to make a new edge and so create that polysurface.

_SplitEdge

You need to split that top surface into two:

You can Split by Isocurve, with the Shrink option set to Yes. Then, you can MatchSrf the respective edges.

-Sky

I would simply create a 4-sided surface on the left side and a 3-sided one on the right side.