How to add image size into shortcode?

Hi, I’m not that good at php and am struggling to work out how to add an image size into this:

add_shortcode( 'taxonomy-image', 'get_category_image' );
function get_category_image($atts){
    $get_image = z_taxonomy_image_url($atts['term_id'] );
    return $get_image;
}

I guess is is something to do with the $atts ? somewhere I need to add the image size.

I hope someone can help, many thanks!

https://ww.wp.xz.cn/plugins/taxonomy-images/