Replace Minimal Zerif 'Big Title' with logo instead

I need help replacing the Big Title in the theme Minimal Zerif with my logo instead. I am a complete newbie, please be patient with me!

I can see from other posts that I’m required to create a child theme and then edit the Big Title php to include my logo. Minimal Zerif seems to already be a child theme so I take it this step is already complete?

What do I edit in the Big Title php? and do I need to change the style CSS also? Thank you!