ajax call in magento 2 - ajax

Question

I have created a custom module in Magento2 where currently I'm selecting a customer and entered multiple order numbers, it will saved into a custom table in the database.
Currently I have to entered order numbers in a textarea but now I want to display all orders after choosing the customer which are not in Complete status.
From this section admin choose orders by clicking on the right side checkbox and Saved it.
Can anyone help me to solve this problem?
Existing Module’s Layout
Want to modify the above layout to the following one: In this desired system when admin change the customer name order numbers associated with that customer will be listed.
New invoice
Code I have used to create the customer dropdown field:
$fieldset->addField('customer_id', 'select', array(
'label' => __('Customer'),
'name' => 'customer_id',
'title' => __('Customer'),
'values' => $this->getCustomerOptionArray()
));
protected function getCustomerOptionArray()
{
$options = array();
$options[] = array(
'value' => 0,
'label' => __('Select Customer'),
);
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$customerObj = $objectManager->create('Magento\Customer\Model\Customer')->getCollection();
foreach ($customerObj as $customerObjdata ){
$options[] = array(
'value' => $customerObjdata->getId(),
'label' => $customerObjdata->getName(),
);
}
return $options;
}