How to have a title and meta description model

Hello,

We would love to help you further.

You can try the following code to output the value of that custom field in a variable called %field-city_name%:

// Custom variable for the custom field from the wp_postmeta table

 add_action( 'rank_math/vars/register_extra_replacements', function(){
   rank_math_register_var_replacement(
       'field-city_name',
       [
        'name' => esc_html__( 'Field City Name', 'rank-math' ),
        'description' => esc_html__( 'Get the field city name from database', 'rank-math' ),
         'variable' => 'field-city_name',
         'example' => 'field_city_name_callback()',
       ],
       'field_city_name_callback'
   );
});
function field_city_name_callback() {
   return get_post_meta(get_queried_object_id(), 'city_name', true);
}

To know, how to insert the code on your website. Please follow the steps from this Knowledge Base article here:
https://rankmath.com/kb/wordpress-hooks-actions-filters/

We hope this information helps. If you need further assistance, please don’t hesitate to contact us.

Thank you.