User roles and hidden fields

Good afternoon! I am using Ultimate Member on my site. I would like to add a hidden field to the default registration form that sets the community role. I tried adding this:

add_action(‘um_after_register_fields’, ‘add_a_hidden_field_to_register’);
function add_a_hidden_field_to_register( $args ) {
echo ‘<input type=”hidden” name=”role_select” id=”role_select” value=”Teacher” />’;
}

to the ultimate-member/core/um-actions-register.php page, but couldn’t get it to work. Can someone tell me where to add it, or give any suggestions? Thanks!