Changes to a Magento 2 Extension

General information for the website: Make some changes to a Magento 2 Extension
Description of requirements/features: See attached file to understand what I want.

I have a Magento 2 Extension developed where I select a customer from dropdown and then enter some order ids for that customer. Then I click on "Save Invoice" to generate a single invoice for all the order ids entered.

Now, Instead of entering the order ids manually, I want to get a list of incomplete/pending orders (using AJAX) when a customer is selected from the dropdown. Then, using checkbox, I should be able to select the orders and click on "Save Invoice"

All the extension functionality should remain as it is. Only, instead of entering order ids manually, the list of pending orders should come up when a customer is selected from dropdown.
Extra services needed: Customization
Extra notes: See attached file to understand what I want. I will initiate discussion with only those candidates who have read the requirements.