gistfile1.txt

var customerRefund = nlapiCreateRecord('customerrefund');

customerRefund.setFieldValue('customer', '111736');
customerRefund.setFieldValue('currency', '1');
customerRefund.setFieldValue('account', '217');
customerRefund.setFieldValue('trandate', new Date());
customerRefund.setFieldValue('paymentmethod', '14');

const creditCount = customerRefund.getLineItemCount('apply');
const creditMemoIndex = customerRefund.findLineItemValue('apply', 'internalid', '4498596');
console.log(creditMemoIndex)
for (let record = 1; record <= creditCount; record++) {
    if (customerRefund.getLineItemValue('apply', 'internalid', record) == '4498596') {
      customerRefund.selectLineItem('apply', record);
      customerRefund.setCurrentLineItemValue('apply', 'apply', 'T');
      customerRefund.commitLineItem('apply');
      break;
    }
}

var customerRefundId = nlapiSubmitRecord(customerRefund, false, true);
console.log(customerRefundId);