WooCommerce Custom Tab with ACF Repeater Field

I believe you need to use get_sub_field() for the repeater field (designer_achievements) and get_field() for its parent. Please take a look at the ACF documentation for the Repeater field’s subfield.

You will also need to use a have_rows() loop, as noted in the documentation.

if( have_rows('parent_field') ):

    while( have_rows('parent_field') ) : the_row();

        $value = get_sub_field('sub_field');

    endwhile;

endif;