Thank you so much for your query.
Can you please check once by changing the height and width of the custom-logo section on functions.php file of the theme.
Check responsive.css file line 96 and 162 and change image with to 100%.
Example code snippit,
Hope, this will solve your problem.
Note: Child Theme is recommended to customize the theme. https://www.templatesell.com/blog/child-themes-and-its-usage/
Let us know if you have any further query.