var targetTime = new Date();
targetTime.setMinutes(targetTime.getMinutes() + targetTime.getTimezoneOffset())
let soRec = record.load({
type:'salesorder',
id:51451//internal is of sales order
});
soRec.setSublistValue({
sublistId: 'item',
fieldId: 'requesteddate',
line: 0,
value: targetTime
});
soRec.save()