Adjusting header and footer

Hello,
I am totally new to WordPress and will try to describe my issue as best I can. I know there is a lot for me to learn, so I’ll just try start at the beginning…

I believe I am using version 5.5.3

I am trying to build my own website and am using Elementor and Astra Sites which I believe to be called plugins(?)

In one of the pre-built sited I installed, I am trying to customize the header and footer of the site but I don’t seem to be able to affect any changes. I’ve watched many videos on customizing the header and footer but don’t seem to be able to do what they are doing.

Any suggestions will be appreciated!
Peter

The page I need help with: [log in to see the link]