How to edit blog theme on "Fixer"

Hi! Good morning!
I'm new on wpmudev, and i'm having some trouble with the "Fixer" theme. I have the main website but it has created another page: https://nataliacss.000webhostapp.com/blog . How can i edit the theme for this page/blog?

I'm sorry but i coudn't find it any answers in here. Thank you so much!