Array (
            [30] => Array (
                [user_id] => 2
                [product_id] => 4080
            )
            [31] => Array (
                [user_id] => 5
                [product_id] => 2942
            )
            [32] => Array (
                [user_id] => 4
                [product_id] => 9630
            )
            [33] => Array (
                [user_id] => 3
                [product_id] => 2542
            )
            [34] => Array (
                [user_id] => 7
                [product_id] => 1234
            )
        )

global $wpdb;

        //Retrieve the bids from the database.
        $form_entries = $wpdb->get_results('SELECT * FROM '. $wpdb->prefix .'frm_item_metas WHERE field_id in (145,147)');

        $data = array();

        foreach ( $form_entries as $meta ) {

            if ( ! isset($data[$meta->item_id])){

                $data[$meta->item_id] = array();

            }

            $data[$meta->item_id][] = $meta->meta_value;

        }

        //rename the array keys
        foreach( $data as &$new_values ) {
          $new_values['user_id'] = $new_values[0]; unset( $new_values[0] );
          $new_values['product_id'] = $new_values[1]; unset( $new_values[1] );
        }
        unset($new_values);

    }

Array (
            [30] => Array (
                'user_id' => '2',
                'product_id' => '4080',
            )
            [31] => Array (
                'user_id' => '5',
                'product_id' => '2942',
            )...