Use action hook wpda_before_simple_form to add HTML and JavaScript before a data entry form. Argument $self contains a reference to your simple form instance, which allows you to interact with your data entry form through public members and methods.
function myform_elements( $self ) {
// Add you HTML and JavaScript here...
}
add_action( 'wpda_before_simple_form', 'myform_elements', 10, 1 );
