Child theme CSS

Hello,
sorry for my English, I would like to create a child theme but I have a problem modifying the font-family of the site title. In fact this is set through the customizer and in the Ashe theme code the function that generates the relative CSS is in a PHP file that is included in the functions.php and which I suppose is executed after any function that I can define in the functions.php of the child theme (or in a file included in it). Is there a way to override that CSS rule without changing the Ashe theme but acting exclusively in the child theme code?