сan’t edit the main page with WordPress

Hi, I have built my site mostly using Colibri Pro plugin. However, I like to now and then edit with WordPress editor, which pop-ups and works for all my pages but the main page. How do I fix it? What is the issue?
I discovered the issue by wanting to add PositiveSSL seal, but I can’t find where I can get to the main page or it’s code.
Thank you

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