So it requires PHP, this article explains the two options of adding it:
https://docs.generatepress.com/article/adding-php/
And this is the function you would add to either your child theme functions file or the codwe snippets plugin:
add_filter( 'generate_start_widget_title', 'widget_title_start_tag' );
function widget_title_start_tag()
{
return '<h4 class="widget-title">';
}
add_filter( 'generate_end_widget_title', 'widget_title_end_tag' );
function widget_title_end_tag()
{
return '</h4>';
}