Change curvature on lofted surfaces.

Hello, what's the technique to adjust and manipulate surfaces at a specific region? I need fi. to be able to change the curvature of the 'belly' portion in the corner of the surface without necessairily changing the slider for the 'B.E.L.L.Y.H.E.I.G.H.T.'

I've managed to select the points of the inner side surface of the open Brep, so what's next? Can I manipulate certain points and rebuild the surface?

Kindest regards, Luc Bossuyt.