How to find easy way to do this

First of all I’m sorry for my bad English.

I try to make this model

I try to integrate these 2 object to be a cap of model. I try to blend surface

But, my result be like this

Please guide me an easy way. I’m new for Rhinoceros. Please help :confounded:

From what I understand of the picture, it seems like you need a cylinder there between your two objects, not a blend.

How do you do like this sir?

I try many times but my result can’t be a surface:confounded:

My original fileblend surface.3dm (40.7 KB)