Need help finalizing epub

I published Garage Band Theory a little over two years ago, and it's doing OK on Amazon and elsewhere.

I've just finished updating all the links, fixing a few typos and some other little things in Sigil.

I'm an author/musician, not an 'ebook builder' and there are a couple things that I haven't been able to figure out ... I think it's pretty simple stuff, but I'm busy with other aspects of the project.

Wondering if there's someone here who can help finish it up.

Thanks,
Duke Sharp
ds@garagebandtheory.com