Customer/Order CSV Export: Instantiate Custom Data Store

functions.php

<?php

function get_custom_csv_export_data_store( $slug ) {

	if ( 'my-custom-data-store' === $slug ) {
		
		require_once 'path/to/csv_export_custom_data_store.php';
		
		return new Custom_CSV_Export_Data_Store();
	}
}
add_filter( 'wc_customer_order_csv_export_custom_data_store', 'get_custom_csv_export_data_store' );