So, using Explode command, we will explode our body polysurface into surfaces. Then we will work on inner shell, so you can hide outer surfaces so they don’t get in the way.
The yellow selected surface is the surface we need to modify a bit. It should be bigger. So the blend surface next to it needs to be deleted, and on this yellow surface we need to extract edges, so we will use DupEdge command.
Move the inner circle like on the image 37
Delete the surface between two circles. Then, using ExtrudeCrv command, extrude that circle to the other circle.
Using PlanarSrf command, make two planar surfaces out of two circles you created earlier with DupEdge.