download csv file in js display timestamp is not same with database

my Program is connection with firebase,in firebase the sensor timestamp is utc+8.but in my program to download csv file the time is display utc+0.how can i improve my program to let that csv file the time is UTC+8.

    default: {
        let csv = `uFEFF${['Timestamp'].concat(dataFields).join(',')}n`;
        for (const dataDocSnap of dataQrySnap.docs)
            if(dataDocSnap.get('object.data')) {
                csv += [dataDocSnap.get('timestamp').toDate().toISOString()]
                    .concat(dataFields.map((dataField) => dataDocSnap.get(`object.data.${dataField}`)))
                    .join(',') + 'n';
            }
        res.header('Context-Type', 'text/csv');
        res.attachment(`${sensorDocSnap.get('name') ?? sensorDocSnap.id}-${date.toFormat('yyyy-MM')}.csv`);
        res.send(csv);
        return;
    }