It has been a very long time since I used HyperLynx 7.5, so I'm going from memory. I might remember this wrong. After you have all the pins that you want connected to the Touchstone network in the schematic, open the Assign Models window that you showed in the image file. Then the cells in the Circuit Connection column should have drop-down lists of the available pins in your schematic. You can map the S-parameter ports to the schematic pins. See if that works for you.