Unable to customize the website

Hi, For the past couple of months, I have been working on a Blog that is focusing on Downloaders. Its built on Generatepress with GutenBerg. Once I designed the Homepage, I added few widgets as per my choice and also edited the footer area. Now, I am facing 2 issues:-

1. I am unable to re-edit the widgets and Footer area as I can't get the option for it. Its just simply vanished and it is quiet frustrating.
2. cz of the first reason, I am fed up and wanna change the theme as well. But, I am not sure that which theme will go best with this kind of blog. Can you please guide to get the most suitable one.