Extend Surface issues

Hello, I am pretty new to Rhino, I’ve got a basic understanding for it and I have been learning a few of the different tools.
I am currently using Rhino 5, I have used the Extend Surface tool several times but it wont select a specific surface that I am try to get my hands on.
I created the poly by using the Sweep 1 rail, to make a handle for a kettle but now, when I try to select the surface of the with _ExtendSrf nothing happens.

Does anyone know why?
I’m not selecting the wrong surface but it’s just not working.

Thank you.

Depending on how it was created and the input objects, the result of your Sweep might be a polysurface; several surfaces joined together.
You have to extract the surface and maybe untrim it before being able to extend it.