Hi Thomas,
That part of the page isn’t controlled by the theme.
But here’s a suggestion:
You’ll need a plugin that allows you to use rich text editor or HTML on Users > Edit user Biography info.
You can try adding this PHP snippet if you want to run HTML from the Biography info text field.
remove_filter('pre_user_description', 'wp_filter_kses');
add_filter( 'pre_user_description', 'wp_filter_post_kses' );
Allowing HTMLs to run on your biography info field will let you format the description to your preference.