Gravity Forms - get value from field in previous page

functions.php

<?php 
// https://docs.gravityforms.com/gform_pre_render/#3-populate-field-with-values-from-earlier-page
add_filter( 'gform_pre_render_8', 'populate_user_dropdown_info' );
add_filter( 'gform_pre_validation_8', 'populate_user_dropdown_info' );
add_filter( 'gform_pre_submission_filter_8', 'populate_user_dropdown_info' );
//add_filter( 'gform_admin_pre_render_8', 'populate_user_dropdown_info' );

function populate_user_dropdown_info( $form ) {

  $current_page = GFFormDisplay::get_current_page( $form['id'] );
    if ($current_page == 2){
      foreach ( $form['fields'] as &$field2 ) {
        if ($field2->cssClass == 'css_class'){
                $previous_value = rgpost('input_' . $field2->id );
        }
      }
    }
}