Hi Yumikom,
You can create a function to execute the shortcode and add the function name to the callback option of the field custom_html. For example:
function foobar_func( $atts ){
return "foo and bar";
}
add_shortcode( 'foobar', 'foobar_func' );
function show_shortcode() {
echo do_shortcode('[foobar]');
}
Screenshot https://share.getcloudapp.com/9ZudygdW