woocommerce_before_calculate_totals.php

<?php
// Update shipping class if a specific field has any value
// Uncomment line below if you want to check the field for a specific value
add_action( 'woocommerce_before_calculate_totals', function( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) ) {
        return;
    }

   	$target_field_id    = 1642; // the field ID
    $shipping_class     = 'easy'; // the shipping class slug

    $term = get_term_by( 'slug', $shipping_class, 'product_shipping_class' );
    if ( ! $term ) {
        return;
    }

    foreach ( $cart->get_cart() as $cart_item ) {
        if ( empty( $cart_item['product_extras']['groups'] ) ) {
            continue;
        }
        foreach ( $cart_item['product_extras']['groups'] as $group ) {
//        if ( isset( $group[ $target_field_id ]['value'] ) && $group[ $target_field_id ]['value'] === 'Specific Value' ) {
          if ( ! empty( $group[ $target_field_id ]['value'] ) ) {
				        $cart_item['data']->set_shipping_class_id( $term->term_id ); // Set the shipping class ID 
				        $cart_item['data']->save();
                break;
            }
        }
    }

}, 20 );