Could not fix a visual problem on sento theme

Hello there, I just started a new WordPress blog on my civil engineering field, which I actually developed in a local server, and get live in last week. There I am using a free theme (Sento), by Think Up Themes Ltd. After being in a live server, I am facing a visual problem in both desktop and mobile. I am having an extended portion in a header strip. I tried to contact them about this. But they do not provide any support to their free theme. That’s why I am posting my problem to the forum. Because I believe someone in this forum may use this theme or may have some solution to my problem. I don’t have much idea about coding. So if anyone can help me, please explain to me how to solve this. I wish I could attach a screenshot for better understanding my problem.
Many many thanks to you in advance…

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