Problem filling out an area


Howdy boys, I would just like to know how i fill out the part marked in red, so that it’s completely filled.

All i’ve managed to do is “put a lid on it” so to speak, where i’ve not been able to fill out anything.
The final product i’ve tried to achieve is to have a hollow sphere where i can change the width of the walls. <= how i want to do it.


English isn’t my first language so sorry if i phrased things wrong.


Like the inside of the outer circle is filled. And the inside of the inner circle is empty if that makes sense.


if the two dome edges are on the same plane and exploded, just trace a line over the exisitng geometry on both domes and delete the centre face.