How do I create the back layer of the seat

[Mans]

Hello

After a few days effort, labor and exercise I finally could simulate the front layer of the seat approximately, but now I don't know how to create the back layer. Please offer a method that helps me to create the back layer and connect it to the front part

 

[Mans]

Respectfully

I waited for an instruction but as I didn't receive any respond, I had to find an alternative myself and eventually could to recreate the back surface and connect it to the front surface after a lot of examinations that were erroneous often.

However, thank you for other helps