Small custom change to template?

Hi, New WordPress guy here with limited code kung-fu.
I just rebuilt my business website (pianoservice.ca) in WP using a found template of Atomic, which I dig. I have most of the bugs worked out, one thing I would like to do is reduce the size of the title (currently occupied by my name). The issue is that when I view it in portrait view on my phone (Android), it overlaps the menu button, which is not ideal.

The option to reduce the size of the title is not offered in the theme editor, unless obviously I do it right in the code, which is “strongly discouraged”, unless of course you know exactly where to look and what to change. Now that I am 98% happy with the site I would really prefer not to cock it up by incorrectly editing the code!

This is probably cake for a more advanced WP user?