Novice struggling with surface generation issue, seeking guidance

Hello everyone, I’m new to Rhino 7 and I have a modeling case that I’m struggling with. I have three surfaces that I need to generate using the appropriate commands, but I’m particularly confused about how to create the irregular, borderless surface in the middle. Any advice or guidance would be greatly appreciated.

Extract isocurve from adjacent surface (ExtractIsocurve command), extend it, edit it to your taste, and use it as a guide for the new surface.