Problem filling out an area

[try100try]

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.
Screenshot - 1e2caaa3b7c6c86e8f0be65f46ae9c10 - Gyazo <= how i want to do it.

[try100try]

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

[try100try]

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

[whiterabbitdesigncompany]

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.