Requirement
provide an estimate for implementing the ‘search postcode’ feature of: getAddress() – Simple APIs for UK Addresses (see the demo)
Instead of showing the Shipping and Billing fields when checkout page loads:
Full Name
Address Line 1
Address Line 2
Town/City
County/Region
Postcode
Phone number
Show the following:
Full name
Enter your postcode + Find address button
Phone number
When the user enters a postcode and clicks on the Find address button, GetAddress fetches all addresses and displays a select input in focus: ‘Select your address’.
When the user selects their address, all the remaining address fields become visible and automatically filled in.
If the postcode is not found, display: “Address not found. Add address manually”. On clicking ‘add address manually, all hidden address fields become visible’
See demo on this page: https://getaddress.io/

Solution
We need to create an extension for the checkout page address create/edit popup.
we will show the find address option as default for it and will make the address field as disabled. If the user needs to update it manually we can provide the option for Add address manually